Mica - Very thin, glassy, shiny flakes, commonly seen in granite and schist. Mica is often black, but may also be gold or silver colored. The word 'mica' is derived from the German for 'glitter'. Olivine - Notable for its green color. It rarely forms crystals.
Calcite is the main ingredient in limestone, and in Portland cement.
Pure calcite is colorless and transparent, sometimes with rhombus- shaped crystals. Gypsum - A form of calcium sulfate which is the main ingredient in chalk. Gypsum is common in Texas, and it is mined in several places in the state. All of these minerals have a noticeable metallic lustre. It can be easily mistaken for gold.