|South America||Virgem de Lapa, Minas Gerais, Brazil||3" x 2" x 2"|
Many of the specimens in this display were labeled with the words "gem" and "gemmy" by the collector. You have an intuitive idea of what these mean, but what does it really take to be a gem in the world of jewelry?
There are two broad categories of "stones" (cut or polished minerals}: precious gems and semi-precious gems. The number of precious gems recognized is small: diamond, ruby (red corundum), sapphire (any other color of corundum), and emerald (green beryl). Of course, it is not only the striking colors that make gems precious. You may recall, if you have read the "Learn More" for specimen #7) that diamond is number 10 and corundum is 9 on the Mohs scale of hardness. The hardness of beryl is between 7.5 and 8. Thus these minerals resist scratching, which is important for stones to be used in jewelry. To be valuable, they must not have only good color, but be transparent to translucent, be free of unattractive inclusions and imperfections, and be large enough to use effectively. These stones are relatively rare, adding to their value.
The semi-precious gems are less rare, and include some, like hematite and turquoise, that are not translucent, but are very attractive when polished and shaped. There are others, such as lapis lazuli and malachite that are neither translucent nor hard, but can be very useful in some types of jewelry. There are dozens of semiprecious gems - in fact, any attractive mineral specimen can be a semi-precious gem.
"Gemmy" simply means that a crystal has the properties of a gem, except that it contains inclusions or other flaws that diminish its usefulness to the jeweler.