Smoky Quartz gemstone color formation

Smoky Quartz is a variety of Quartz, it is a silicon dioxide mineral ranging in color from pale, smoky gray to deep brown and black, sometimes yellowish-brown. Though Smoky Quartz can be nearly opaque, it is almost always transparent to translucent.  Smoky Quartz offers a rare and beautiful transparency that draws light into shades of black and brown. Smoky Quartz was known as a Stone of Power.  

The color of smoky quartz is caused by irradiation and aluminum impurities built into its crystal lattice to form the color-centers [1].  In normal geological environments, the color centers formation process can only take place at temperatures below 50°C, otherwise the rate of color center destruction surpasses that of color center formation.  Thus the color of smoky quartz crystals appeared long after the crystals have grown. It is estimated that it takes several million years for a crystal to assume a deep color by natural radiation emitted in nearby rocks [2] [3].

The color of smoky quartz is typically much more homogeneous than that of amethyst, but often still more intense at the tips of the crystals. Natural smoky quartz will lose its color when heated to about 200°C, and the color will occur again when the crystal is irradiated with gamma-rays. Some smoky quartz is sensitive to ultraviolet light and will pale when exposed to sunlight for a long time.

At some locations smoky quartz shows zones of violet or yellow color along with smoky ones. The different colors might be found in different layers as "phantoms", or they show a patchy distribution in one crystal.  It is also found Smoky Amethyst Quartz - a combination of Amethyst and Smoky Quartz and Smoky Citrine Quartz - a combination of Citrine and Smoky Quartz.

To artificially irradiate colorless quartz can produce smoky quartz. It's impossible to tell whether the smoky quartz is natural or not just by looking at the crystals. However, natural Smoky Quartz tends to be smoky to the base, whereas irradiated tends to have a white crystal base next to the matrix rock.  Also if it is so black you cannot see through it and it has good surface luster, it is probably irradiated. 

Smoky quartz shows a change of color from yellow-brown to red-brown when turned around an a-axis in polarized light. Like all crystal quartzes, the Smoky quartz has a hardness of 7 on the Mohs scale and is thus insensitive to scratches.

Smoky Quartz is found throughout the world.  It is usually found in intrusive igneous and certain high grade metamorphic rocks as these contain traces of radioactive elements whose radiation causes the coloration. Important deposits exist in Brazil, Madagascar, Mozambique, Australia, Switzerland, Scotland, and the United States (Colorado and New Hampshire).

Smoky Quartz is an affordable gemstone, and is used in various form of gemstone beads jewelry. Smoky quartz is very common and often lacking flaws, it can reach several hundred carats with minimal flaws. High quality Smoky Quartz is usually faceted for ring and pendant centerpieces, and less quality Smoky Quartz is most often used in beads with different shapes:  round, coin, oval, square, pillow, cube, tube, et al. With Smoky Quartz beads in your favorite color and shape, you even can create your own unique piece of Smoky Quartz jewelry, and with plenty of opportunity to customize to fit your unique style. There are plenty of low-cost Smoky Quartz beads available through online store and be sure to check out the discounted Smoky Quartz beads first to start your design.

The fact that Smoky Quartz can lose its color makes it obvious that Smoky Quartz jewelry should not be worn while sunbathing and high temperature can also be harmful to the Smoky Quartz.

Reference:

[1] G.R. Rossman, “Colored varieties of the silica minerals”, Reviews in Mineralogy, Vol.29 

[2] Chudoba, K. F. (1962): Some relations between the causes of amethyst, smoky quartz, and citrine colors as given by modern science. Mineralogicheskii Sbornik (Lvov), (16), 91-105.

[3] Cohen, Alvin J. (1989): New data on the cause of smoky and amethystine color in quartz. Mineralogical Record 20, 365-367.

Difference between Rose Quartz and Pink Quartz

Rose Quartz is the rosy pink variety of Quartz. Its color is usually soft, ranging from very light pink to medium pink in intensity and lack good transparency. It is never transparent, and it does not form single crystals. Rose quartz is usually very evenly colored.  Rose quartz is slightly to highly turbid, indicating the presence of the second phase, namely pink-colored fibrous inclusions [3] [4].

Quartz single crystals of a similar rose color are called pink quartz. The single-crystal pink quartz is photochemically unstable, unlike massive rose quartz, it is extremely rare.

Based on their optical properties and chemical composition, these two types of quartz appears to be of a different nature: (1) the cause of their color is different, (2) pink quartz is sensitive to light, while rose quartz is not, (3) both varieties form in different environments, and (4) pink quartz develops single crystals while rose quartz does not.

In spite of extensive studies over the last century, the source of the rose coloration in quartz still remains a subject of active debate. Many possible mechanisms for the color of rose quartz have been proposed [1], but no consensus has developed. More recently it has been suggested [3] that fibrous inclusions are responsible for color of rose quartz. The nature of the colorizing nanofibers in rose quartz has recently been studied [4], following the more "direct" approach that was already chosen [3], they dissolved rose quartz from various locations in hydrofluoric acid and extracted mats of visually homogeneous, fine textured, flaky pink-colored nanofibers.  The fibrous mineral inclusions are rose-colored mineral and could be a mixture of dumortierite and a related phase. The mineral makes up only about 0.05% - 0.15% of the overall weight of rose quartz. The mineral will bleach when heated above 500°C, but will not regain its color when irradiated. Color loss can be induced by oxidizing agents, too, and heat treatment in a reducing atmosphere will turn heated and paled material rose-colored again.  Experiments also show the embedded mineral fibers are not randomly oriented, but preferrably oriented along specific crystallographic axes.  Thus pink-colored fibrous inclusions cause the coloration of rose quartz.

Pink quartz’s color is caused by small amounts of aluminum, Al⁽⁺³⁾, and phosphorus, P⁽⁺⁵⁾, built pairwise into the crystal lattice to replace Si⁽⁺⁴⁾, and subsequent high energy irradiation [1]. The two electrically neutral SiO₄ groups are replaced by one AlO₄^- and one PO₄⁺ group. Pink quartz is often accompanied by phosphate minerals, like (Mn,Fe)Al[(OH)₂|PO₄]•H₂O.  Many pink quartz is translucent to transparent. Pink quartz is very sensitive to light and will pale quickly in direct sunlight. This is an indication that the color is due to color centers whose formation appears to be triggered by high energy radiation.

Rose quartz occurs at many pegmatite locations all over the world. It is commercially mined in Madagascar, South-Africa, Namibia, U.S.A. (South Dakota), and Brazil (Bahia and Minas Gerais). Star rose quartz is found in South Dakota and Madagascar. Pink quartz was first found in Brazil in 1959 which is still the main source.

Pink Quartz is an extremely rare single crystal and usually cut to make gemstone beads for ring and pendant. Rose Quartz is an affordable gemstone, and is used in various form of jewelry. Rose Quartz is most often used in beads with different shapes:  round, coin, oval, square, pillow, cube, tube, et al. With Rose Quartz beads in your favorite color and shape, you even can create your own unique piece of Rose Quartz jewelry, and with plenty of opportunity to customize to fit your unique style. There are plenty of low-cost Rose Quartz beads available through online store and be sure to check out the discounted Rose Quartz beads first to start your design.

The fact that Pink Quartz can lose its color makes it obvious that Pink Quartz jewelry should not be worn while sunbathing. High temperature can be harmful to the Rose Quartz.

Reference:

[1] G.R. Rossman, “Colored varieties of the silica minerals”, Reviews in Mineralogy, Vol.29 

[2] Maschmeyer, D., Lehmann, G. (1983) A trapped-hole center causing rose coloration of natural quartz. Zeitschrift für Kristallographie, 163: 181-186.

[3] Applin, K.R., Hicks, B.D. (1987) Fibers of dumortierite in quartz. American Mineralogist, 72, 170-172

[4] Goreva, J.S., Ma, C., Rossman, G.R. (2001) Fibrous nanoinclusions in massive rose quartz: The origin of rose coloration. American Mineralogist, 86: 466-471.

[5] Hori, H. (2001) Nomenclature of Quartz Color Variation: Pink and Rose. Mineralogical Record, 32(1). 

Type II quartz colored varieties gemstone - Color caused by inclusions

Quartz is the second most abundant mineral in the Earth's continental crust with an overall formula SiO₂. Rock crystal can be found in some form in any geological environment that allows the formation of quartz in general. Large, well-formed and transparent crystals can be found. For nice crystals to form, conditions in a geological environment need to change more or less gradually and slowly over a long period of time.  A single rock crystal may have grown over a period of several million years during the uplift and folding of the mountains.

There are many different varieties of quartz, common colored varieties include citrine, rose quartz, amethyst, smoky quartz, blue quartz, and others, which are semi-precious gemstones. The color formation of rock crystal’s varieties will be reviewed as following.

For Rose quartz, in spite of extensive studies over the last century, the source of the rose coloration in quartz still remains a subject of active debate. Many possible mechanisms for the color of rose quartz have been proposed, but no consensus has developed. More recently it has been suggested  that fibrous inclusions are responsible for color of rose quartz. The nature of the colorizing nanofibers in rose quartz has recently been studied, following the more "direct" approach that was already chosen, they dissolved rose quartz from various locations in hydrofluoric acid and extracted mats of visually homogeneous, fine textured, flaky pink-colored nanofibers.  The fibrous mineral inclusions are rose-colored mineral and could be a mixture of dumortierite and a related phase. The mineral makes up only about 0.05% - 0.15% of the overall weight of rose quartz. The mineral will bleach when heated above 500°C, but will not regain its color when irradiated. Color loss can be induced by oxidizing agents, too, and heat treatment in a reducing atmosphere will turn heated and paled material rose-colored again.  Experiments also show the embedded mineral fibers are not randomly oriented, but preferrably oriented along specific crystallographic axes.  Thus pink-colored fibrous inclusions cause the coloration of rose quartz.

Aventurine is a variety of translucent poly-crystal quartz with inclusions of minerals.  It is fundamentally different from Amethyst which is also a variety of quartz with the presence of manganese and iron in quartz, the manganese and iron are impurities in atomic level to form new energy states (color centers) that produces the purple color. In Aventurine case, the inclusions of minerals are much larger particles which reflect light that enters the quartz and produce a sparkly appearance.  The common color of aventurine is green and red orange, but it may also be brown, yellow, blue, or purple.

Green aventurine is a variety of translucent poly-crystal quartz with inclusions of Fuchsite, also known as chrome mica, is a chromium (Cr) rich variety of the mineral muscovite, belonging to the mica group of phyllosilicate minerals, with the following formula: K(Al,Cr)₂(AlSi₃O₁₀)(OH)₂, which display apple green color.  Bright reflection light from apple green Fuchsite inclusions inside quartz produce a sparkly silvery green appearance for green aventurine.

For red orange and brown aventurine, the colors are attributed to inclusions of red orange hematite and brown hematite inside quartz.  Hematite is the mineral form of iron oxide (Fe₂O₃), colored black to steel or silver-gray, brown to reddish brown, or red.  Bright reflection light from red orange hematite or brown hematite inclusions inside quartz produce a sparkly red orange and brown appearance for red orange and brown aventurine.

For yellow aventurine, the colors are attributed to inclusions of Pyrite. The mineral pyrite, or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula FeS₂. This mineral's metallic luster and pale brass-yellow hue give it a superficial resemblance to gold, hence the well-known nickname of fool's gold. Bright reflection light from golden Pyrite inclusions inside quartz produce a sparkly yellow appearance for yellow aventurine.

For blue aventurine, the colors are attributed to inclusions of blue Dumortierite . Dumortierite is a fibrous variably colored aluminium boro-silicate mineral, Al₇BO₃(SiO₄)₃O₃.  The crystals are varied in color from brown, blue, and green to more rare violet and pink. Substitution of iron and other tri-valent elements for aluminium result in the color variations. Bright reflection light from blue Dumortierite inclusions inside quartz produce a sparkly blue appearance for blue aventurine.

For purple aventurine, the colors are attributed to inclusions of purple Lepidolite.  Lepidolite is a lilac-gray to rose-colored member of the mica group with formula K(Li,Al,Rb)₃(Al,Si)₄O₁₀(F,OH)₂. Bright reflection light from purple Lepidolite inclusions inside quartz produce a sparkly purple appearance for purple aventurine.

There are three type of Blue quartz: Type I: Blue color of single crystals quartz is due to Rayleigh scattering effect.  The Rayleigh scattering is the scattering of light by particles much smaller than the wavelength of the light.  It is the scattered light by small particles in the atmosphere that gives the blue sky. In blue quartz case, the light is scattered by abundant submicrometer-sized inclusions inside quartz crystal to cause sky blue color. The total amount of inclusions in the blue quartz is calculated to be 0.02 %. This is the rarest form of blue quartz, and this type of blue quartz exhibits a particularly beautiful blue coloration, which is sky blue in the center of each crystal and darker at the margins.  In addition, in certain orientations these crystals display an intense silver-blue chatoyant flash.

Type II: Blue color of single crystal quartz is due to evenly distributed inclusions of blue minerals, like magnesio-riebeckite or tourmaline. The blue color is caused by light reflection  of the included blue minerals, however the inclusions are individually too large (~0.1 x 1 x 20 μm) to contribute to the blue color by Rayleigh scattering.

Type III: Blue color of ploy-crystal quartz is due to inclusions of blue minerals, the inclusions of blue minerals have much larger size than the size of inclusions in type I and type II.  This type of blue quartz is similar to blue aventurine that is also colored by embedded blue minerals, like dumortierite. In general, blue quartz has less blue inclusions and shows light blue color with blue pattern.  Blue aventurine has more blue inclusions and shows evenly distributed dark blue color. There is no clear boundary between type III blue quartz and blue aventurine.

Rutilated quartz is a variety of Quartz with needle-like rutile inclusions, embedded in it. The rutile needles can be reddish, golden or silvery.

Colored Quartz is an affordable gemstone, and is used in various form of jewelry.  High quality colored Quartz is usually faceted for ring and pendant centerpieces, and less quality colored Quartz is most often used in gemstone beads for jewelry design.

Type I quartz colored varieties gemstone - Color caused by color center

"Rock Crystal" is the name for clear, colorless pure quartz crystal. Quartz is the second most abundant mineral in the Earth's continental crust with an overall formula SiO₂. Rock crystal can be found in some form in any geological environment that allows the formation of quartz in general. Large, well-formed and transparent crystals can be found. For nice crystals to form, conditions in a geological environment need to change more or less gradually and slowly over a long period of time.  A single rock crystal may have grown over a period of several million years during the uplift and folding of the mountains.

There are many different varieties of quartz, common colored varieties include citrine, rose quartz, amethyst, smoky quartz, blue quartz, and others, which are semi-precious gemstones. The color formation of rock crystal’s varieties will be reviewed as following.

Amethyst has been known as the most highly prized form of quartz. The color can vary from a pale purple to a dark purple. Very often the color is unevenly distributed and is most intense at the tips of the crystals.  Amethyst owes its color to the presence of iron built into its crystal lattice. Some of this iron sits in sites normally occupied by silicon and some is interstitial. The iron impurity is usually in the +3 valence state to substitute Si.  For natural amethyst, Gamma ray radiation from nuclear decay in the surrounding rocks can make charge transfer from an iron lattice site to an interstitial iron, and form +4 valence state of iron (purple color centers). This +4 iron absorbs certain wavelengths (357 and 545 nanometers) of light causing the purple color. It is needed to have quartz that contains the right amounts of iron and then is subjected to enough natural radiation to cause the color centers to form. 

Citrine is the yellow to brownish-red variety of the Quartz.  Citrine’s yellow color is caused by quantities of Fe³⁺ impurities which form color center inside quartz’s lattice. However, Citrine is somewhat rare in nature.  Most citrines on the market have been heat treated from amethyst or smoky quartz. Natural Citrine is yellow to orange-yellow, and occurs in much lighter hues than the heat-treated material, which is dark orange-brown to reddish-brown. Virtually all heat-treated material has a reddish tint, whereas the natural specimens do not.

Inexpensive amethyst is often heated at high temperatures to produce the more profitable orange yellow citrine. Amethyst has been known has iron impurities at +4 valence state.  Iron +4 valence state related purple color centers are not as stable as iron +3 related yellow color centers at high temperature, thus at high temperature only more stable yellow color centers exist to produce yellow color.  Citrines whose colors have been produced by artificial means tend to have much more of an orange or reddish caste than those found in nature, which are usually a pale yellow.  In some Amethyst deposits, the Amethyst has been partially or fully changed over to yellow Citrine by natural means of heating. It is relatively well known that the vast majority of citrine quartz is the product of heat treating amethyst. Material from Brazil and Uruguay has often been used for this purpose. Both large and small amethyst-lined geodes are converted to citrine using simple low-temperature heat treatment in air. Citrine made by heating amethyst may be returned to a purple color by bombarding it with radiation which cause color centers transfer back to purple color centers.

Ametrine contains both amethyst and citrine in contact with one another.  The colors of amethyst and citrine are produced by iron impurities with different oxidation states within the quartz.  Purple is thought to be produced by Fe⁴⁺ related color centers, of which the Fe impurities are oxidized to Fe⁴⁺ by natural radiation emitted in nearby rocks. The golden-yellow is thought to be produced by Fe³⁺ related color centers. The different oxidation states occur due to there being a temperature gradient across the crystal during its formation and by natural radiation.  The concentration of iron is much higher in the yellow than in the purple sectors. If heating up a natural Ametrine, only the purple sectors loose their color, and the result is a crystal with 3 almost colorless and 3 yellow sectors. 

The color of smoky quartz is caused by irradiation and aluminum impurities built into its crystal lattice to form the color-centers.  In normal geological environments, the color centers formation process can only take place at temperatures below 50°C, otherwise the rate of color center destruction surpasses that of color center formation.  Thus the color of smoky quartz crystals appeared long after the crystals have grown. It is estimated that it takes several million years for a crystal to assume a deep color by natural radiation emitted in nearby rocks.

Pink quartz’s color is caused by small amounts of aluminum, Al⁽⁺³⁾, and phosphorus, P⁽⁺⁵⁾, built pairwise into the crystal lattice to replace Si⁽⁺⁴⁾, and subsequent high energy irradiation. The two electrically neutral SiO₄ groups are replaced by one AlO₄^- and one PO₄⁺ group. Pink quartz is often accompanied by phosphate minerals, like (Mn,Fe)Al[(OH)₂|PO₄]•H₂O.  Many pink quartz is translucent to transparent. Pink quartz is very sensitive to light and will pale quickly in direct sunlight. This is an indication that the color is due to color centers whose formation appears to be triggered by high energy radiation.

Colored Quartz is an affordable gemstone, and is used in various form of jewelry.  High quality colored Quartz is usually faceted for ring and pendant centerpieces, and less quality colored Quartz is most often used in gemstone beads with different shapes:  round, coin, oval, square, pillow, cube, tube, et al. With colored Quartz beads in your favorite color and shape, you even can create your own unique piece of colored Quartz jewelry, and with plenty of opportunity to customize to fit your unique style. There are plenty of low-cost colored Quartz beads available through online store and be sure to check out the discounted colored Quartz beads first to start your design.

Citrine and its relation with amethyst gemstone

Citrine is the yellow to brownish-red variety of the Quartz. Quartz is a chemical compound of silicon and oxygen, silicon dioxide SiO₂, commonly called silica. If pure, quartz is a colorless, transparent, and very hard crystalline material of glass-like look.  Citrine’s yellow color is caused by quantities of Fe³⁺ impurities which form color center inside quartz’s lattice. However, Citrine is somewhat rare in nature.  Most citrines on the market have been heat treated from amethyst or smoky quartz. Natural Citrine is yellow to orange-yellow, and occurs in much lighter hues than the heat-treated material, which is dark orange-brown to reddish-brown. Virtually all heat-treated material has a reddish tint, whereas the natural specimens do not.

Inexpensive amethyst is often heated at high temperatures to produce the more profitable orange yellow citrine [1][2]. Amethyst has been known has iron impurities at +4 valence state.  Iron +4 valence state related purple color centers are not as stable as iron +3 related yellow color centers at high temperature, thus at high temperature only more stable yellow color centers exist to produce yellow color.  Citrines whose colors have been produced by artificial means tend to have much more of an orange or reddish caste than those found in nature, which are usually a pale yellow.  In some Amethyst deposits, the Amethyst has been partially or fully changed over to yellow Citrine by natural means of heating. It is relatively well known that the vast majority of citrine quartz is the product of heat treating amethyst. Material from Brazil and Uruguay has often been used for this purpose. Both large and small amethyst-lined geodes are converted to citrine using simple low-temperature heat treatment in air. Citrine made by heating amethyst may be returned to a purple color by bombarding it with radiation which cause color centers transfer back to purple color centers.

Some smoky quartz can be turned into citrine by careful heating at a high temperature [3][4][5].  The color of smoky quartz is caused by irradiation and traces of aluminum built into its crystal lattice. Aluminum replaces silicon to form a [AlO₄]^- group instead of [SiO₄].  Since the yellow color centers are often more stable than the smoky color centers, thus some smoky quartz can be turned into citrine by careful heating.  This type of citrine is colored by aluminum-based and irradiation-induced color centers related to those found in smoky quartz. Citrine produced by heat-treating Smoky Quartz sometimes has a "smoky" hue to it, and can be border lined between Citrine and Smoky Quartz, with either definition being correct.

Natural Citrine is not common and occurs sparingly in many large Quartz deposits. Most commercial gem-grade material comes from Rio Grande do Sul and Minas Gerais, Brazil, but almost all of the Brazilian material is heat treated Amethyst.
A classic exhausted locality for natural Citrine is Olkhovka in the Northern Ural Mountains, Russia. Other locations where natural Citrine is found is San Cristobal, Santander, Colombia; Lubumbashi in Katanga (Shaba), Congo (Zaire); Antananarivo Province, Madagascar; Salamanca, Spain; and Dauphine, France.

There are not many yellow gemstones in the world of jewels. A diamond or a sapphire or a topaz may be yellow - those will be expensive. However, the citrine fulfills everyone's color wishes, from lemon yellow to reddish brown. Citrine is often used as an inexpensive substitute for Topaz.

High quality Citrine is usually faceted for jewelry and less quality Citrine is most often used as gemstone beads with different shapes:  round, coin, oval, square, pillow, cube, tube, et al.

Reference:

[1] Chudoba, K. F. (1962): Some relations between the causes of amethyst, smoky quartz, and citrine colors as given by modern science. Mineralogicheskii Sbornik (Lvov), (16), 91-105.

[2] Lehmann, G. (1972): Yellow color centers in natural and synthetic quartz. Physik der Kondensierten Materie 13, 297-306.

[3] Maschmeyer, D. et al (1980): Two modified smoky quartz centres in natural citrine. Phys.Chem.Minerals (6), 145-156

[4] Schmetzer, K. (1988): Thermal stability of yellow color centers in natural citrine. Neues Jahrbuch für Mineralogie, Monatshefte 2, 71-80.

[5] Rossman, G.R. (1994): Colored varieties of the silica minerals. In: Reviews in Mineralogy, Vol.29, Silica - Physical behavior, geochemistry and materials applications, Mineralogical Society of America.

Three type Blue Quartz gemstone

Blue quartz is a group blue variety of quartz.  This rather open definition is due to the fact that no blue quartz has been found in nature with unique cause of coloration, there are no blue color center in quartz lattice to produce blue color.  So it is fundamental different from Amethyst’s color formation which is produced by purple color center [1].  Thus blue quartz has several different types [2][3]:

Type I: Blue color of single crystals quartz is due to Rayleigh scattering effect.  The Rayleigh scattering is the scattering of light by particles much smaller than the wavelength of the light.  It is the scattered light by small particles in the atmosphere that gives the blue sky. In blue quartz case, the light is scattered by abundant submicrometer-sized inclusions inside quartz crystal to cause sky blue color. The total amount of inclusions in the blue quartz is calculated to be 0.02 %. This is the rarest form of blue quartz, and this type of blue quartz exhibits a particularly beautiful blue coloration, which is sky blue in the center of each crystal and darker at the margins.  In addition, in certain orientations these crystals display an intense silver-blue chatoyant flash.

Type II: Blue color of single crystal quartz is due to evenly distributed inclusions of blue minerals, like magnesio-riebeckite or tourmaline. The blue color is caused by light reflection  of the included blue minerals, however the inclusions are individually too large (~0.1 x 1 x 20 μm) to contribute to the blue color by Rayleigh scattering.

Type III: Blue color of ploy-crystal quartz is due to inclusions of blue minerals, the inclusions of blue minerals have much larger size than the size of inclusions in type I and type II.  This type of blue quartz is similar to blue aventurine that is also colored by embedded blue minerals, like dumortierite. In general, blue quartz has less blue inclusions and shows light blue color with blue pattern.  Blue aventurine has more blue inclusions and shows evenly distributed dark blue color. There is no clear boundary between type III blue quartz and blue aventurine.

It is believed that Blue Quartz is a soothing and calming stone, bringing a relaxing, peaceful vibe to any situation. Like all crystal quartzes, the blue quartz has a hardness of 7 on the Mohs scale and is thus insensitive to scratches.

Blue quartz occurs at many localities in worldwide. In USA, One famous localities is in Llano County Texas where it is found as small doubly terminated crystals in a rhyolitic porphyry called, informally, llanoite. The crystals weather loose and can be collected easily. Blue quartz is found in Wisconsin, most notably in a diorite exposed by the Dairyland Power Dam near Tony.

High quality Blue Quartz (Type I and II) are usually faceted for ring and pendant centerpieces, and less quality Blue Quartz (Type III) is most often used in gemstone beads .

Reference:

[1] G.R. Rossman, “Colored varieties of the silica minerals”, Reviews in Mineralogy, Vol.29 

[2] Jayaraman, N. (1939). The cause of colour of the blue quartzes of the charnockites of South India and the Champion Gneiss and other related rocks of Mysore. In Proceedings of the Indian Academy of Sciences, Section A (Vol. 9, No. 3, pp. 265-285). Indian Academy of Sciences.

[3] Pacns, J. B. (1988). Origin and significance of blue coloration in quartz from Llano rhyolite (llanite), north-central Llano County, Texas. American Mineralogist, 73, 313-323.

Aventurine gemstone and color formation

Aventurine is a variety of translucent poly-crystal quartz with inclusions of minerals.  It is fundamentally different from Amethyst which is also a variety of quartz with the presence of manganese and iron in quartz, the manganese and iron are impurities in atomic level to form new energy states (color centers) that produces the purple color. In Aventurine case, the inclusions of minerals are much larger particles which reflect light that enters the quartz and produce a sparkly appearance.  The common color of aventurine is green and red orange, but it may also be brown, yellow, blue, or purple.

Green aventurine is a variety of translucent poly-crystal quartz with inclusions of Fuchsite, also known as chrome mica, is a chromium (Cr) rich variety of the mineral muscovite, belonging to the mica group of phyllosilicate minerals, with the following formula: K(Al,Cr)₂(AlSi₃O₁₀)(OH)₂, which display apple green color.  Bright reflection light from apple green Fuchsite inclusions inside quartz produce a sparkly silvery green appearance for green aventurine.

For red orange and brown aventurine, the colors are attributed to inclusions of red orange hematite and brown hematite inside quartz.  Hematite is the mineral form of iron oxide (Fe₂O₃), colored black to steel or silver-gray, brown to reddish brown, or red.  Bright reflection light from red orange hematite or brown hematite inclusions inside quartz produce a sparkly red orange and brown appearance for red orange and brown aventurine.

For yellow aventurine, the colors are attributed to inclusions of Pyrite. The mineral pyrite, or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula FeS₂. This mineral's metallic luster and pale brass-yellow hue give it a superficial resemblance to gold, hence the well-known nickname of fool's gold. Bright reflection light from golden Pyrite inclusions inside quartz produce a sparkly yellow appearance for yellow aventurine.

For blue aventurine, the colors are attributed to inclusions of blue Dumortierite . Dumortierite is a fibrous variably colored aluminium boro-silicate mineral, Al₇BO₃(SiO₄)₃O₃.  The crystals are varied in color from brown, blue, and green to more rare violet and pink. Substitution of iron and other tri-valent elements for aluminium result in the color variations. Bright reflection light from blue Dumortierite inclusions inside quartz produce a sparkly blue appearance for blue aventurine.

For purple aventurine, the colors are attributed to inclusions of purple Lepidolite.  Lepidolite is a lilac-gray to rose-colored member of the mica group with formula K(Li,Al,Rb)₃(Al,Si)₄O₁₀(F,OH)₂. Bright reflection light from purple Lepidolite inclusions inside quartz produce a sparkly purple appearance for purple aventurine.

The majority of green and blue-green aventurine originates in India. Creamy white and red orange material is found in Chile, Spain and Russia.

Aventurine is a popular gemstone because of its beauty and also because it is not highly priced.  Aventurine is formed into gemstone beads for jewelry making.

Aquamarine gemstone beads & coloration

Aquamarine is an affordable gemstone belonging to the Beryl family (chemical formula Be₃Al₂(SiO₃)₆). Pure Beryl is colorless.  However, some impurities cause the diverse amount of colors and many varieties. The pale blue color of aquamarine is attributed to iron impurities’ ions Fe²⁺.  The Fe³⁺ ions produce golden-yellow color, and when both Fe²⁺and Fe³⁺ are present, the color is a darker blue due to Fe²⁺-O-Fe³⁺ inter-valence charge transfer.  Aquamarine ranges in color from a faint light blue to blue and bluish-green, due to the concentration of iron impurities and its ions valence state, with lighter colored stones being the more common type.

The green hues in most Aquamarine can be removed through heat treatment. Its color fades to white when exposed to sunlight or is subjected to heat treatment. Natural Aquamarine is usually lighter and greener in color, and heat treatment creates deeper bluer hues due to change of iron impurities’ ions valence state.

Aquamarine has good hardness (7.5 to 8 on the Mohs scale), the hardness makes it very tough and protects it to a large extent from scratches, but it may develop internal cracks if banged hard.  Aquamarine is belonging to hexagonal crystal group, its moderate refraction and its weight in common with the other members of Beryl family.

Aquamarine gemstone is mined mainly in Brazil, but also is found in Nigeria, Madagascar, Zambia, Pakistan, and Mozambique. In the United States, aquamarines can be found at the summit of Mt. Antero in the Sawatch Range in central Colorado. In Wyoming, aquamarine has been discovered in the Big Horn Mountains.

The largest aquamarine of gemstone quality ever mined was found in Marambaia, Minas Gerais, Brazil, in 1910. It weighed over 110 kg, and its dimensions were 48.5 cm x 42 cm.

High quality flawless single crystal aquamarine is cut to form gemstone beads to maximize the intensity of its color, and to display cat's eye effect and asterism.  Lesser quality poly-crystal aquamarines lacking good transparency are formed into stone beads with different shapes.

Ametrine gemstone beads color formation

Ametrine contains both amethyst and citrine in contact with one another.  The colors of amethyst and citrine are produced by iron impurities with different oxidation states within the quartz [1].  Purple is thought to be produced by Fe⁴⁺ related color centers, of which the Fe impurities are oxidized to Fe⁴⁺ by natural radiation emitted in nearby rocks. The golden-yellow is thought to be produced by Fe³⁺ related color centers. The different oxidation states occur due to there being a temperature gradient across the crystal during its formation and by natural radiation.  The concentration of iron is much higher in the yellow than in the purple sectors. If heating up a natural Ametrine, only the purple sectors loose their color, and the result is a crystal with 3 almost colorless and 3 yellow sectors.

If a well-formed Ametrine crystal is sawn perpendicular to the c-axis, the color zones of amethyst and citrine often form a geometric pattern that radiates outwards from the c-axis like the pieces of a pie. Straight-line contacts separate zones of amethyst from zones of citrine.  These crystals usually contain zones of clear quartz, amethyst and citrine. When these crystals are cut into pieces that are appropriately sized for faceting gemstones, only a portion of the stones will be Ametrine. The remainder will be amethyst, citrine, and clear quartz [2].

Laboratory experiments in 1981 determined that heat and irradiation can be used to convert natural amethyst into a bicolor material that has an appearance similar to natural Ametrine [4].  Since 1994, a Russian laboratory has perfected the industrial production of bicolored quartz crystals that are later irradiated to bring out the typical Ametrine colors [3] to form Ametrine gemstone beads for jewelry.

Like all crystal quartzes, the Ametrine has a hardness of 7 on the Mohs scale and is thus insensitive to scratches.

Ametrine is rarely found in nature. The only known and well confirmed location for Ametrine is an area in Bolivia near the Brazilian border [2]. It's commercially exploited and almost all of the world's commercial natural Ametrine production has been from the Anahi  Mine in southeastern Bolivia.

High quality Ametrine is usually faceted for jewelry and less quality Ametrine is most often used as stone beads with different shapes:  round, coin, oval, square, pillow, cube, tube, et al. With Ametrine beads in your favorite color and shape, you even can create your own unique piece of Ametrine jewelry, and with plenty of opportunity to customize to fit your unique style. There are plenty of low-cost Ametrine beads available through online store and be sure to check out the discounted Ametrine beads first to start your design.

Reference:

[1] G.R. Rossman, “Colored varieties of the silica minerals”, Reviews in Mineralogy, Vol.29 

[2] Vasconcelos P, Wenk HR, Rossman GR (1994) The Anahí ametrine mine,
Bolivia. Gems and Gemology 30, 4-23.

[3] Balitsky VS, Lu T, Rossman GR, Makhina IB, Mar'in, AA, Shigley JE, Elen S,
Dorogovin BA (1999) Russian synthetic ametrine. Gems and Gemology 35,
122-134.

[4] Balitsky, V. S.; Machina, I. B.; Mar'in, A. A.; Shigley, J. E.; Rossman, G. R.; Lu, T. (2000): Industrial growth, morphology and some properties of Bi-colored amethyst-citrine quartz (ametrine). Journal of Crystal Growth 212, 255-260.

What cause Amazonite stone beads blue color

Amazonite is a popular gemstone usually varies in color from yellow-green to blue green and may also exhibit fine white streaks.  It was named after Amazon River, from which certain green stones were formerly obtained, however it is doubtful whether Amazonite occurs in the Amazon area. 

Amazonite is green to blue-green variety of Microcline.  Microcline (KAlSi₃O₈) may be clear, white, pale-yellow, brick-red, or green color depends on the impurities which contain. Common Impurities inside Microcline are Fe, Ca, Na, Li, Cs, Rb, H₂O, Pb.   The source of amazonite’s color was uncertain for years, and many assumed the color was due to copper, which often produces blue and green colors in gems and minerals.  However, studies [1] suggest that the blue-green color caused by an elevated content of Pb and water in the Microcline. In the past two to three decades, some inconsistencies with this possible correlation have become apparent.  Analyses by Hoffmeister and Rossman (1985) determined that some samples of green amazonite did indeed have a high lead concentration, whereas some non-green samples of microcline also had unexpectedly high lead concentrations. They propose that while lead does indeed play a role in coloring amazonite, both natural radiation and structural water are necessary to produce monovalent or trivalent lead for color of amazonite. Therefore the color of amazonite could possibly be due to three variables: lead, water and a form of ionizing radiation.  More recent studies [2] suggest that the green color would arise from the ion Pb⁺, whereas the blue one would be attributed to the ion Pb³⁺. Thus the blue-green color is due to mixture of Pb⁺ and Pb³⁺.

Amazonite often has white lines or alternating streaks mixed in, and can have uneven color distribution. A deep forest-green color is most preferred, but Amazonite gemstones can also be light green and bluish-green.  Grayish-green and very faint green stones also exist, but are not commonly used as gemstones.  

Sunlight can sometimes enrich the color of genuine amazonite.  Amazonite’s color is lost on heating to over 300°C and can be restored by irradiation if heating was insufficient (<500°C) to cause water loss. It has a hardness range of 5 to 6 on the Mohs Scale.  Care should be handled with Amazonite as it is sensitive to pressure and can easily crack or chip. 

Because of its bright green or blue-green color when polished, amazonite is sometimes cut and used as gemstone beads, although it is easily fractured.  You will not see amazonite very often in the current market. It makes some very pleasing jewelry items but is kind of hard to find.

Amazonite is an inexpensive gemstone is most often used in stone beads with different shapes:  round, coin, oval, square, pillow, cube, tube, et al. With Amazonite beads in your favorite color and shape, you even can create your own unique piece of Amazonite jewelry, and with plenty of opportunity to customize to fit your unique style. There are plenty of low-cost Amazonite beads available through online store and be sure to check out the discounted Amazonite beads first to start your design.

Reference:

[1] Brightwell, Stephanie, 1999; "Coloration due to Lead Levels in Blue microcline Feldspar (Amazonite) from the Morefield Pegmatite, Amelia, Virginia",

[2] Julg, A. (1998): A theoretical study of the absorption spectra of Pb+ and Pb3+ in site K+ of microcline: application to the color of amazonite. Physics and Chemistry of Minerals 25, 229-233. 

Amethyst gemstone color formation

Amethyst has been known as the most highly prized form of quartz. The color can vary from a pale purple to a dark purple. Very often the color is unevenly distributed and is most intense at the tips of the crystals.  Amethyst owes its color to the presence of iron built into its crystal lattice [3]. Some of this iron sits in sites normally occupied by silicon and some is interstitial. The iron impurity is usually in the +3 valence state to substitute Si.  For natural amethyst, Gamma ray radiation [1] [2] from nuclear decay in the surrounding rocks can make charge transfer from an iron lattice site to an interstitial iron, and form +4 valence state of iron (purple color centers). This +4 iron absorbs certain wavelengths (357 and 545 nanometers) of light causing the purple color. It is needed to have quartz that contains the right amounts of iron and then is subjected to enough natural radiation to cause the color centers to form. 

The most famous and commercially important amethyst locations are in volcanic rocks. Amethyst is also found in igneous, and certain metamorphic rocks, as those contain enough radioactive trace elements for a sufficient irradiation of the crystals.  As the iron is built into the crystal lattice, amethyst is sometimes found in ore deposits. Sometimes amethyst banded with purple and white lines. 

Amethyst is crystalized Silicon Dioxide belong to hexagonal crystal group, its moderate refraction and its weight in common with the other quartzes. Amethyst’s Hardness is 7, and can be melted at 1650 degree and is insoluble in common solvents. It has been known that the amethyst changes its color on being heated above 250 degree due to charge transfer from iron +4 valence states to +3 valence states, and the color become darker under irradiation due to more charge transfer from iron +3 valence states to +4 valence states.

Synthetic amethyst can be produced by irradiation of clear quartz to form iron +4 valence state (purple color centers), and the clear quartz has been first doped with iron impurities. On exposure higher temperature above 250 degree, the irradiation effects can be partially cancelled and the amethyst generally becomes yellow or even green.

Amethyst is a very common mineral and is found worldwide. The deposits with the greatest economic significance are in various states in southern Brazil and in Uruguay.  The third major export country is Madagascar. Good amethyst was found in Aztec graves, though the deposits from which they were extracted are no longer known today. On the Canadian side of Lake Superior in North America, there is a place named Amethyst Harbor. The violet quartz is found there in ample quantities, though rarely in gemstone quality.

Brilliant purple amethyst gemstone beads are an eye-catching choice for jewelry. Romantic and passionate amethyst, the traditional birthstone for those born in February, is said to represent courage and inner strength. Amethyst gemstone jewelry makes a thoughtful and personal birthday gift.

High quality amethyst is cut to maximize the intensity of its color. Amethyst is also formed into stone beads with different shapes: round, coin, oval, square, pillow, cube, tube, et al. With amethyst beads in your favorite color and shape, you even can create your own unique piece of amethyst jewelry, and with plenty of opportunity to customize to fit your unique style. There are plenty of low-cost amethyst beads available through online store and be sure to check out the discounted amethyst beads first to start your design.

Do not expose an amethyst to direct sunlight for a long time. Very likely it will pale out by the ultraviolet radiation. Some amethyst pales out really quickly and some very slowly, but you can't tell in advance. Thus amethyst jewelry should not be worn while sunbathing, and sudden changes of temperature can also be harmful to the amethyst.

[1] G.R. Rossman, “Colored varieties of the silica minerals”, Reviews in Mineralogy, Vol.29 

[2] Nassau, K. (1975a) The origins of color in minerals and gems. Lapidary J., 29, 920-8, 1060-70, 1250-8, 1521.

[3] E.F. Holden, The cause of color in smoky quartz and amethyst, American Mineralogist, Vol.9, 203-252, 1925