Glorius Garnets

摘要

The garnets are silicate minerals, forming a group with a shared crystallographic structure but with wide variation in chemical composition. What all of them have in common is a very regular framework structure of silicon and oxygen atoms, often giving rise to their characteristically very symmetrical crystals. Most are isometric (cubic crystal system, although the rare garnet-family member henritermierite is tetragonal), and they are relatively hard and brittle, with no cleavage planes. As a result, crushed garnet makes a good abrasive, and is still used to make some grades of "sand paper". Most of us are familiar with garnets as red, dodecahedral crystals, but they occur in all colours of the rainbow except blue.