Silicates—including quartz, mica, olivine, and precious minerals such as emeralds—are ... or the type of mark, or streak, that they leave when rubbed on a laboratory tool called a streak ...

Quartz, felspar and mica are found in pegmatite rocks, which are an important source of many critical minerals such as beryl, lithium, niobium, tantalum, molybdenum, tin, titanium and tungsten ...