Nonmetallic minerals are useful due to their physical properties but are not used for the extraction of metals. Most nonmetallic minerals are rock-forming minerals, and some are nonmetallic ore minerals, but some are industrial raw materials by themselves, such as quartz, calcite, feldspar and kaolinite. Most gemstones and jades come from nonmetallic minerals, such as diamonds, rubies, emeralds, jadeites and nephrites. Some nonmetallic minerals are used to extract nonmetallic elements, such as the extraction of phosphorus from apatite. The physical properties of nonmetallic minerals are generally the opposite of those of metallic minerals. They have no lustre, poor conductance and low thermal conductivity, and they are transparent or translucent when cut into 0.03-mm-thick slices and observed under a microscope. Their crystal families and crystalline aggregates can be important ornamental stones.