Orthoclase feldspar is a well known mineral and a common constituent found in many igneous rocks. It has two cleavage planes, which are at right angles to one another, resulting in the crystals breaking into rhombic forms and is the reason for its naming, being derived form the ancient Greek wording for "straight fracture." It is often pink in colour but can be white or pale grey. It is fairly hard at 6 - 6.5 on the Moh's scale of hardness and has a vitreous lustre, which means it shines or reflects light. Orthoclase is commonly found in many granitic rocks, being one of the main constituent minerals, the other two being quartz and mica. It is also common in felsic rocks such as rhyolite. These specimens are supplied by weight, upto 1 kilograms and come supplied in a polythene bag with an information label, the sizes of the pieces inside vary between 20 mm to 80 mm.