![]() Orbicular jasper has spherules of banded agate in a jasper matrix. The colors may be very strong, especially shades of brown, yellow, red, and green. Jasper: Usually a mass of tiny silica crystals pigmented by impurities. Lace agate is from Mexico, Arizona, and Namibia (blue). ![]() Banded agate is from Brazil, Uruguay, Madagascar Mexico, and the United States. Scenic agates are from Yellowstone National Park, Wyoming and Montana. Occurrence: Moss agates are from India, Scotland, and the northwestern United States. ritella agate is composed mostly of shells and shell fragments of the gastropod Tirrritella and certain other species.Shell agate is patterned by silicified shells in the rock. Fire agate has platy crystals of iron oxide layered with chalcedony, resulting in iridescence brought out by cutting and polishing. Lace agate is banded with intricate swirls and loops. Scenic agates have inclusions that look like pictures of scenery, with lakes, shorelines, trees, and shrubs. The MOSS agates have mossy inclusions of mineral oxides. Banded agates have regular color layers and bright colors. ![]() Also mossy or dendritic inclusions, sometimes creating the impression of landscapes, vegetation, and, so forth. Banded varieties, or materials with mosslike inclusions, are known as agate.Īgate: Usually takes the form of colored layers or ) ands, flat or concentric. The solid-colored materials are mostly chalcedony stained by oxides and are referred to as jaspers. Names within the cryptocrystalline quartz family are generally based on colors and patterns. The most generally widespread of these materials is composed of tiny fibers of silica and is known as chalcedony. Deposition within a spherical cavity, such as a gas pocket in basalt or other volcanic rock, results in concentric banding also seen in agates.Ĭryptocrystalline quartz varieties offer a huge diversity of patterns and colors. This latter type of deposition results in banding that is seen in certain types of agate. They form either as gelatinous masses that slowly dehydrate and crystallize or by deposition from slowly percolating groundwaters, depositing silica over a long period of time. The name Rock crystal is from the Greek krystallos, meaning ice, because the Greeks thought it was ice frozen forever hard by an unnatural frost created by the gods.Occurrence: Hot Springs, Arkansas Herkimer New York Swiss Alps Minus Gerais, Brazil Japan Madagascar New South Wales, Australia Upper Burma Canada.Ĭryptocrystalline quartz varieties are colored chiefly by mineral impurities in the growth environment, including oxides of Fe, Mn, Ti, Cr, Ni, and other elements. There are many types of mineral inclusions known. The material is common and has little intrinsic value, except in very large, flawless pieces. ![]() Rock Crystal: Used in faceted gems, beads, carving, decorative objects, and lamps. The only color varieties that do not form such large crystals are amethyst and rose quartz. As a result of slow crystal growth, many such crystals achieve great internal perfection and yield enormous pieces of faceting rough. The colored, crystalline quartz varieties generally occur in pegmatites and veins, having been deposited from water solutions over a long period of time. The color origins in crystalline quartz are complex and are only now beginning to be fully understood. The crystalline varieties are those that occur in distinct, visible crystals: ame thyst, smoky quartz, citrine, rose quartz, and milky quartz. Quartz comes in a vast array of colors and shapes (when in crystals), and the cryptocrystalline varieties offer an almost endless spectrum of color and patterns. It is this kind which, when first time discovered in Alps, was believed to be a form of frozen water and therefore called crystal. When quartz is pure in composition, it is entirely devoid of color and almost water-clean in its limpidity. Quartz or silica is composed of silicon (Si) and oxygen (O), the two most abundant elements in the crust of the Earth (with \(SiO_2\) chemical formula).
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