Joel E. Arem

I explored this work as a step toward understanding What humans are doing with precious stones -- objects treasured in every culture across the world. Early man found mineral fragments in stream beds and fields, on mountain slopes, in barrens and caves. Early on their were ornaments. Then they took on religious significance - hundreds of minerals are mentioned in the Bible and in the Bagavad-ghita.

Modern gemology is a relatively recent development. The internal structure of crystals and metals is even yet being explored. In 1914 X-rays revealed the atomic geormetry of crystals for the first time.

There is now an unprecedented demand for gems. This encyclopedia provides information about the mineral species which have been cut as gems. But what IS a gem?

According to accepted practice, the material must have Beauty, Durability, and Scarsity. Opal has always been considered a gem because of its beauty, but it is fragile, and soft (5.5 on Mohs scale). Proustite, a silver arsenic sulfide, is seldom faceted, but it can be, and its red color surpasses rubies. But many dispute whether it is a gem!
Zoisite was not bothered with prior to the 1960s, until Tiffany & Co noted that it resembles sapphire, and marked the new material as "tanzanite". It is now accpted as a gem.

There are 3000 known minerals. Note the "synthetic" and cultured (pearls) varieties, and simulants, such as cut colored glass. This encyclopedia includes 250 species, and "any mineral species can be considered a gemstone if suitable cutting material can be found". [xi,a]

Every mineral is characterized by definite crystalline structure and chemical composition that varies within defined limits.[xi,b].

Three Rock Types (examples): Igneous (granite), Sedimentary (sandstone), Metamorphic (slate).

Scarsity. Only one painite (looks like ruby), and very few taafeites, have ever been found. [xvii]… (altro)

The book takes a logical approach. First is a general introduction to the breadth of the topic. Then the book goes into mineral, how they form and their differences. Then it lists minerals. After that it discusses the common types of rocks, breaks those types down further. Finally it lists the types of rocks. There are pictures for the rock and minerals. At the end are tables to aid in identification. Finally, an index is present as well.

The inside cover boasts a retail price under two dollars which, even back in 1973 was inexpensive for the amount of information in the book.… (altro)