- a greenish micaceous mineral consisting essentially of a hydrous silicate of potassium, aluminum, and iron and occurring in greensand, clays, etc.
- a green mineral consisting of the hydrated silicate of iron, potassium, aluminium, and magnesium: found in greensand and other similar rocks. Formula: (K,Na,Ca) 0.5-1 (Fe,Al,Mg) 2 (Si,Al) 4 O 10 (OH) 2 .nH 2 O
