Amethyst and Citrine are the most popular and valuable gem varieties of Quartz, but other forms also make important gemstones. Chalcedony describes any form of Quartz that is microcrystalline, in compact form without any visible crystals.What is the heat tolerance of quartzite?
Heat Tolerance: Quartz tends to be more heat resistant than other stone surfaces. That does include granite, limestone, marble and others. These stones can withstand temperatures up to just under 300 degree Fahrenheit.