Diaspore, or diasporite, is an aluminium oxide hydroxide mineral having the orthorhombic crystal system. It occurs as colourless to pinkish or yellowish lamellar crystals, often with a flattened appearance. It occurs in metamorphic and crystalline rocks but also in weathered clay deposits and limestones. This specimen, actual width 140 mm, is from the Chester Emery mines in Chester, Massachusetts, USA.