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| Garnet |
| The Garnet group of minerals show crystals with a habit of dodecahedrons and trapezohedrons. They are nesosilicates with the same general formula, A3B2(SiO4)3. Many different chemical elements are included in the several varieties of garnet, including calcium, magnesium, aluminium, iron2+, iron3+, chromium, manganese and titanium. Garnets show no cleavage, but do show a dodecahedral parting. |
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| Feldspar |
| Feldspar (from the German Feld, field, and Spat, a rock that does not contain ore) is the name of an important group of rock-forming minerals which make up perhaps as much as 60% of the Earth's crust. They crystallize from magma in both intrusive and extrusive rocks; they occur as compact minerals, as veins, and are developed in many types of metamorphic rock. They may also be found in many types of sedimentary rock. |
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| Chrysoprase |
| Chrysoprase is a semi-precious form of quartz, green in color and translucent. It is cryptocrystalline in nature, which means that it is comprised of crystals so fine that they cannot be seen as distinct particles under normal magnification. |
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| Chrysocolla |
| Chrysocolla (hydrated copper silicate) is a mineral, CuSiO3·nH2O. It is of secondary origin and forms in the oxidation zones of copper ore bodies. Associated minerals are quartz, limonite, azurite, malachite, cuprite, and other secondary copper minerals. |
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| Aquamarine |
| Aquamarine is gemstone-quality blue beryl, closely related to the emerald. Aquamarines can be found in the United States in Colorado at the summit of Mt. Antero in the Collegiate Range in central Colorado. In Brazil, there are mines in the states of Minas Gerais, Espírito Santo and Bahia. |
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| Amethyst |
| Amethyst is a violet or purple variety of quartz often used as an ornament. The name is generally said to be derived from the Greek a, "not," and methuskein, "to intoxicate," expressing the old belief that the stone protected its owner from drunkenness. It was held that wine drunk out of a cup of amethyst would not intoxicate. However, the word may probably be a corruption of an Oriental name for the stone. |
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| Agate |
| Agate (ag' it) is a term applied not to a distinct mineral species, but to an aggregate of various forms of silica, chiefly Chalcedony. According to Theophrastus the agate (achates) was named from the river Achates, now the Drillo, in Sicily, where the stone was first found. |
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| Topaz |
| The mineral topaz is a silicate of aluminium and fluorine with the chemical formula (AlF)2SiO4. It is orthorhombic and its crystals are mostly prismatic terminated by pyramidal and other faces, the basal pinacoid often being present. |
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| Turquoise |
| Turquoise (or turquois) is an opaque, blue to green hydrated copper aluminium phosphate mineral according to the chemical formula CuAl6(PO4)4(OH8)8·5H2O. It is rare and valuable in finer grades and has been enjoyed as a gem and ornamental stone for untold thousands of years, owing to its unique colour. In recent times turquoise—like most other opaque gems—has had its popularity undermined by the introduction of myriad treatments, imitations, and so-called synthetics onto the market, some difficult to detect even by experts. |
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| Quartz |
| Quartz is the second most abundant mineral in the Earth's crust. It has a hexagonal crystal structure made of trigonal crystallized silica (silicon dioxide, SiO2), with a hardness of 7 on the Mohs scale. Density is 2.6g/cm³. The typical shape is a six-sided prism that ends in six-sided pyramids, although these are often distorted, or so massive that only part of the shape is apparent from a mined specimen. Additionally a bed is a common form, particularly for varieties such as amethyst, where the crystals grow up from a matrix and thus only one termination pyramid is present. A quartz geode consists of a hollow rock (usually with an approximately spherical shape) with a core lined with a bed of crystals. |
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