Tuesday, 5 February 2013

Discovery And Recovery of Crystal

Blue crystals of liroconite, a copper arsenate, from a secondary-enriched layer
THE SEARCH FOR MINERAL deposits including metals and gemstones has been taking place since prehistoric times. Some, such as copper, occur in great quantity; others, such as silver, gold, and diamond are found in much smaller quantities but fetch higher prices. If mining is to be profitable, large quantities of the mineral must occur in one area and be relatively easy to extract, either by surface quarrying, panning and dredging, or if necessary by deep mining. Minerals from which useful metals such as copper, iron, and tin are extracted are called ores.

Growing from seed

RICH VEIN Larger concentrations of ore occur in veins, but most high-grade ores have been found and in many cases worked out. Ores in veins are usually worked by deep mining. This vein in altered granite contains ;.chalcopyrite and quartz.
SCIENTISTS HAVE TRIED TO MAKE CRYSTALS like those found in the Earth's crust for well over a century. Natural crystals often contain impurities or are flawed in some way, but synthetic ones can be made flawless. They can also be made to grow a particular shape and size for specific needs. In recent times a range of artificial crystals have become important to modern technology. Grown crystals are built into almost every electronic or optical device made today. The need for a huge amount of perfect crystals has led to more and more synthetic crystals being made, and it could be said that future developments in electronics will depend on the development of crystal growing techniques.

Melt technique

LAST TO GO Granite pegmatites characteristically consist of large crystals and are the source of many fine gems, including tourmaline topaz and beryl They are formed by the crystallization of the last fluids left after most of the granite has solidified.
Excellent crystals may be grown by slow cooling or evaporation of a supersaturated solution (no more will dissolve) of a salt such as halite, alum, or ammonium dihydrogen phosphate (ADP). In the experiment shown, powdered ADP containing a small chrome-alum impurity has been completely dissolved in boiling water and then cooled.

Writer - Dr.R.F. SYMES and Dr.R.R. HARDING
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