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Agate: SiO2. A form of quartz which is usually classified as a microcrystalline form of chalcedony which comes in a wide variety of colors and types. Some take the form of exotic bands, which when in parallel and of alternating colors, form onyx and sardonyx. Many agates have a hollow center and beautiful bands of vivid colors throughout the stone. When these take the form of moss like or dendritic growth patterns the stone is sometimes called moss agate. Agate is usually formed by successive deposits within cavities of volcanic rocks.
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Amethyst: SiO2. Amethyst is a violet variety of quartz which and owes its color mostly to iron impurities and other trace elements. It occurs in hues from a light pinkish violet to deep purples and may also exhibit red and blue colors. Arizona is the proud home of Four Peaks Amethyst, regarded as producing some of the highest quality Amethyst gemstone material in the world. Amethyst is also the traditional birthstone for February.
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Azurite: Cu3(CO3)2(OH)2. Azurite and malachite are hydrous silicate form of copper and are found within the copper mines of Arizona. Azurite is the blue carbonate and malachite the green. The two stones are usually very closely associated, and the combination is known as azure-malachite. Malachite is most valuable when it shows rounded shapes and a silky lustre.
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Chalcedony: SiO2. A cryptocrystalline form of silica, composed of very fine intergrowths of the mineral quartz and moganite. Chalcedony has a waxy luster, and may be semitransparent or translucent. It can assume a wide range of colors, but those most commonly seen are white to gray, grayish-blue or a shade of brown ranging from pale to nearly black. Chalcedony occurs in a wide range of varieties and many gemstones such as agate, onyx, chrysoprase and jasper are in fact forms of chalcedony.
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Fire Agate: SiO2. A variety of chalcedony. Fire agate gemstones have beautiful iridescent rainbow colors, similar to opal, with a measurement of hardness on the MOHS scale of between 6.5-7. The vibrant rainbow colors found within fire agates, created by the Schiller effect as found in mother-of-pearl and fire opal, is caused by the alternating silica and iron oxide layers which diffract and allow light to pass which forms the interference of colors known as fire. The fire agate visual effects arise from light interference within the microstructure crystal layering of the gemstone.
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Garnet: X3Z2(SiO4)3. All garnets possess similar physical properties and crystal forms, but differ in chemical composition. Some of the different types of garnets are pyrope, almandine, spessartine, grossular, uvarovite and andradite. Garnet are found in many colors including red, orange, yellow, green, purple, brown, blue, black, pink and colorless. Arizona is best known for it's Anthill Garnets which have vivid, natural red colors, that shine like the brilliant sunshine of the desert Southwest.
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Gold: Au. Gold is a native element and precious metal which has long been prized for its beauty, resistance to chemicals and workability. Gold occurs in different types of deposits. Placer gold is often rounded small grains, flakes and nuggets found in stream and river deposits that have weathered out of the larger bedrock lode deposits. Arizona has a very long history of gold production and it's placer gold has a high purity on average of 89% to 92%.
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Peridot: (Mg,Fe)2SiO4. Peridot, a green colored crystalline variety of the mineral chrysolite or olivine, is a magnesium iron silicate. The gemstone variety of olivine is known as Peridot and the shade of green can vary from a yellow-green to brown-green color, however the most valuable is considered to be the dark olive green. The San Carlos Apache Peridot from Southeastern Arizona is often considered world class gem material. These gem mines on the Peridot Mesa are among some of the largest Peridot deposits in the world. This lovely gemstone, which is August's birthstone, was formed during the volcanic Tertiary Period.
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Turquoise: A hydrated phosphate of copper and aluminum which is a secondary mineral occurring in copper deposits. Designated the official gemstone of Arizona in 1974 turquoise is an opaque, blue to green mineral. Some of the worlds finest quality turquoise comes from the southwesten United States. With names like Sleeping Beauty, Bisbee Blue Spiderweb, and Kingman, these quality gems are sought by jewelers and gem collectors worldwide.
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Vanadinite: Pb5(Vo4)3Cl. A secondary lead mineral usually found in arid climates resulting from the alteration of the sulphides and silicates. Vanadinite is a mineral belonging to the apatite group of phosphates. It is one of the main industrial ores of the metal vanadium and a minor source of lead. A dense, brittle mineral, it is usually found in the form of red hexagonal crystals.
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Wulfenite: Pb(MoO4). A mineral usually found as thin bright orange-red or yellow-orange crystals in oxidized zones of lead deposits. It is sometimes brown, although the color can be highly variable. In its yellow form it is sometimes called yellow lead ore. A noted Arizona locality for wulfenite is the Red Cloud Mine whihc has crystals that are deep red in color and usually very well-formed.
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