Minerals jasper

Seawater contains only 2-14 ppm of SiOj and is far below saturation with respect to amorphous silica (34). Part of this is suspended fragments of siliceous organisms (35). Siever has pointed out that the major mechanism for the predpitation of silica on the surface of the earth is biochemical (36). The various organisms responsible for silica deposition were reviewed by Voronkov, Zelchan, and Lukevits (4a). The microcrystalline quartz minerals jasper and chalcedony are probably transformation products of very early diatomite deposits. About two-thirds of the deposited silica is from diatoms and the remainder from radiolaria and sponges. 

Silicon makes up 25.7% of the earth s crust, by weight, and is the second most abundant element, being exceeded only by oxygen. Silicon is not found free in nature, but occurs chiefly as the oxide and as silicates. Sand, quartz, rock crystal, amethyst, agate, flint, jasper, and opal are some of the forms in which the oxide appears. Granite, hornblende, asbestos, feldspar, clay, mica, etc. are but a few of the numerous silicate minerals. 

By cyanos, Dioscorides, as Theophrastus and Pliny, means our lapis lazuli, and by armenion our azurite, both being blue-colored minerals. Pliny refers to these also. Cyanos, he refers to as a kind of iaspis (jasper) of a blue color, and armenium as a mineral of blue color, thinner in color and cheaper than coeruleum. 

Next to materials of the glass-ceramics type, many varieties of chalcedony, such as agate, carneol, onyx, sardonyx, heliotrope and jasper, exhibit similar changes in hardness resulting from different consolidation of the cryptocrystalline structure of silica among mineral individuals. 

Lapis lazuli is a deep blue gemstone that is a complex copper silicate mineral varying widely in composition. It often contains sparkles of iron pyrite or calcite. The best source is probably Afghanistan. A pale blue variety is found in Chile. Some material sold as lapis lazuli is actually artificially colored jasper from Germany. 

Jade is the common name for gem-quality specimens of two distinctly different mineral species, jadeite and the massive variety of actinolite, called nephrite. The word jade is derived from the Spanish piedra deyjada, meaning stone of the flank. This refers to its popular use as a cure for diseases of the kidneys and liver. Other minerals that have been mistaken for jade, or used as jade imitations include green jasper (quartz), vesuvian (idocrase), massive grossular garnet, chloromelanite (a mixture of dark pyroxenes) (Table 2.10). 

Stn. Silica.—This acid is found pure in rock crystal, or in white quartz. Along vrith small and variable quantities of certain metallic oxides it forms many well-known minerals—as yellow or smoke rock crystal with oxide of iron agate, jasper, heliotrope, camelian, with the same metal amethyst with oxide of manganese prase with oxide of nickel rose-quartz with some fugitive colouring matter opal and calcedony with water, c. c. Many sands and sandstones are nearly pure silica, and quartz rock and flint are quite pure. 

Mineralization occurs (a) in east-west veinlets and veins varying from a few centimetres to a few metres in width they occur together between levels 80 and 40 m and beyond up to the surface, forming a locally very rich stockwork, and (6) in the fractures of the filon-toit -BN6 and filon-mur systems, where mineralized veins show thicknesses from several metres to a few tens of metres carrying sooty pitchblende, hexavalent uranium minerals in a jasper and banded quartz gangue. 

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