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. The crystals can vary in size and the largest one discovered to date was found in the Ural mountains, Russia, measured 10 x 10 x 4 meters and weight around 100 tons. These particular mineral samples were collected by staff from Evje, Norway and are available in various sizes, each sample will come supplied in a card tray with an information label.