Gemstones and Their Origins by Peter C. Keller Ph.D. (auth.)

By Peter C. Keller Ph.D. (auth.)

Each gem deposit-whether of fundamental foundation within the guardian rocks; or secondary as alluvial placers in valley flooring, river gravels, or the sand of oceanic cabinets­ provides an eloquent chronicle of the Earth's lifestyles tale. It finds to the professional the prodigious tactics which shaped the current crust of our planet, of which this quantity discloses a small yet fascinating element. The fabrics of the Earth's crust are the rocks. during this booklet, the writer expounds on how they have been shaped, why they altered, why they grew to become the cradles of valuable gems, how they're categorised, and the way they're now exploited through guy. What initiates the expansion of gems? How do they crystallize? Why do gem stones of a similar species, originating from diverse resources, fluctuate? What explanations the incidence of sorts? Why do diamonds, not like different necessary stones, happen now not close to the Earth's floor in its crust, yet deep down underneath it within the top mantle? those are just a number of the entrancing matters mentioned during this enlightening quantity. The reader learns that the Earth is strangely alive and changing constantly-sometimes via sluggish and equable adjustments and now and then via violent and super cataclysms, occasions from which gem stones issue.

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S' GUEAEARO. MEXICO MExICO Topaz '. IGONHA. NMU'-' CHI NA Peridot A_MURS1NKA,. USSR MOZAMBIQUE DO • • ~ \J 0 O'~ ANAK' E. QUEENSLANO. AUSTRALIA Sapphire Zircon :.. ~ " V ery hot water vapors escaping from magmas deep in the earth's crust are known as hydrothermal fluids (from hydro, meaning "water," and thermal, meaning "hot"). These fluids often carry rare elements, such as fluorine and beryllium, away from the magma via fractures in surrounding rocks and sometimes combine with near-surface water to pick up additional elements.

The two processes may or may not be separated by a long period of time. Most fissure veins are narrow and range in length from a few feet to a few miles. Usually, the fissure veins are found in groups that form systems. Although many factors may be involved in hydrothermal deposition, including chemical reactions similar to those responsible for turquoise and malachite at lower temperatures, the most important factors are changes in temperature and pressure. In general, a drop in temperature and/or pressure decreases a mineral's solubility and causes crystallization.

According to the better records that have been kept since then, South Australia produced $204 million in opal up to 1977, and an average of about $40 million annually since 1977 (Barnes and Townsend, 1982). An excellent discussion of the famous opals of Australia can be found in Leechman (1961). By far the most spectacular and famous opals are the incredible black opals from Lightning Ridge. The Butterfly or Red Admiral stone from Lightning Ridge is considered to be one of the most beautiful opals in the world.

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