Gem Focus January 2019: Garnets
*Gem Focus & Market Pulse (Free Subscriber)There are many ways we think of garnet: as the birthstone for January, or as an affordable alternative to ruby. We may perceive it as a collection of shiny burgundy beads for fun jewelry. To the ancients, garnets had even greater value. From the small tumbled beads put in gold necklaces in pre-dynastic Egypt in 4th millennium BC, to beautifully carved garnet intaglios excavated throughout the vast Roman Empire, one can sense the significance that this material represented in these cultures. More garnets are seen in Europe around and after Alexander the Great’s invasion of Persia, later trade becomes more regular between Greeks, Asian and African cultures.
Modern mineralogy identifies garnet as a mineral group containing 24 related species. Of these, fewer than 10 are known as gemstones. Due to their complex structure, garnets are one of the most intriguing mineral groups. Structurally similar, gem garnets differ from one another by interchanging chemical compositions through solid solutions. Garnet group minerals possess high refractive index and display high vitreous luster that is unmistakable to the trained eye.
Red garnets generally contain fissures and fractures due to their formation. The irregular structure of these fissures and fractures also creates weakness in the stone. Conchoidal breaks, chips or even deep cavities can occur easily during or after fashioning of garnets.
Garnets grow in various genetic processes of the igneous and metamorphic cycles. They occur in basic igneous rocks, granites, pegmatites, schists, certain marbles and…