Mimetite is a lead arsenate chloride mineral formed as a secondary deposit in the oxidized zones of lead deposits, usually as small hexagonal prisms. The color varies from pale to bright yellow, to orange to brown, even gree or white. The name means “imitator”, in reference to it’s resemblance to pyromorphite.
Pb5(AsO4)3Cl; Hardness 3½ - 4; Hexagonal
Calcite forms in many different geologic environments. Usually colorless or white it can occur in many tints due to the inclusion of minor constituents during formation. It has possibly more habits of occurrence than any other mineral.
CaCO3 Hardness 3; trigonal
Goethite is the yellow- or reddish-brown alpha polymorph of iron(III) oxide-hydroxide, typically occurring in low-temperature environments. Goethite has been well known since ancient times for its use as the pigment brown ochre. The mineral was named after the Johann Wolfgang von Goethe
α-Fe3+O(OH); Hardness 5 - 5½; Orthorhombic
Gypsum commonly forms in several environments, ranging from sedimentary evaporite deposits to hydrothermal vein deposits. It can occur in massive granular form (alabaster), translucent white crystals (selenite is one variety), and as desert “roses.” It has extensive practical uses, such as fertilizer (for sulfur) and as building material (plaster of Paris, dry wall). Giant crystals of gypsum occur in Mexico’s Cave of Crystals and Cave of Swords.
CaSO4 · 2H2O; Hardness 2; Monoclinic