Quartz

The wikipedia article on quartz indicates that the luster of quartz is "vitreous/glossy". Do you see a problem there? If not, keep reading. The word "vitreus" in Latin means glass. (You could have seen that coming if you knew that glass translates as vidrio in Spanish, or vidro in Portuguese.) (Other languages show similarities, no doubt.) And what is glass? Well, there are many types of glass such as soda-lime glass, and Pyrex, but glass all has the same fundamental ingredient: silicon dioxide, SiO2. Now, if we took pure Si02 and grew it into a big single crystal and stuck it somewhere, say in a rock, and let you find it on the ground, you know what we would call it? That's right, quartz. So, wikipedia is offering the very insightful description that quartz, which is essentially naturally occurring glass, has a vitreous or glassy luster. Brilliant.