Anhydrite is a mineral consisting of sulphate of lime. It has rectangular cleavage fragments and occurs in a manner similar to gypsum and often found with it but not as common. It is found in the cap rock of salt domes and in limestone rocks. The name comes from the Greek meaning 'without water' . It has the formulae CaSO4 and a relative hardness of 4. Research Anhydrite
Augite is an important rock forming mineral of the pyroxene group. Chiefly found in dark coloured igneous rocks, especially those whose magmas were rich in iron, calcium and magnesium. Seldom found in rocks that contain much quartz. A common member of the pyroxene group. Told from the amphibole group by cleavage. It has the formulae (Ca,Na) (Mg,Fe,Al,Ti)(Si,Al)2O6 and a relative hardness of 6. When crystallized it assumes the form of short, slightly rhombic prisms, with their lateral edges replaced, and terminated at one or both extremities by numerous planes. A transparent green variety found at Zillerthal, in the Tyrol, is used in jewelry. Research Augite
In geology, clay-slate is a rock consisting of clay which has been hardened and otherwise changed, for the most part extremely fissile and often affording good roofing-slate. In colour it varies from greenish or bluish grey to lead colour. The cleavage is independent of the stratification. It rarely lies parallel to the bedding, generally crossing the strata at all angles. Research Clay-Slate
Cleavage is the structural lines along which a mineral will break up when it is subjected to pressure, such as being struck a sharp blow. The regular structure of most crystallized bodies becomes manifest as soon as they are broken. Each fragment presents the form of a small polyhedron, and the very dust appears under the microscope an assemblage of minute solids, regularly terminated. The directions in which such bodies thus break up are called their planes of cleavage; and the cleavage is called basal, cubic, diagonal, or lateral (or peritomous), according as it is parallel to the base of a crystal, to the faces of a cube, to a diagonal plane, or to the lateral planes. In certain rocks again there is a tendency to split along planes which may coincide with the original plane of stratification, but which more frequently cross it at an angle. This tendency is the consequence of the readjustment by pressure and heat of the components of rocks, which is one of the phases of metamorphism. Research Cleavage
Cronstedtite, named after the Swedish mineralogist Cronstedt, is a mineral consisting principally of silicate of iron, and crystallizing in hexagonal prisms with a perfect basalcleavage. Research Cronstedtite
In geology, the term foliation refers to the property, possessed by some crystalline rocks, of dividing into plates or slabs, which is due to the cleavage structure of one of the constituents, as mica or hornblende. It may sometimes include slatey structure or cleavage, though the latter is usually independent of any mineral constituent, and transverse to the bedding, it having been produced by pressure. Research Foliation
Heulandite, named after the English mineralogist Heuland, is a mineral of the Zeolite family, often occurring in amygdaloid, in foliated masses, and also in monoclinic crystals with pearlylustre on the cleavage face. It is a hydrous silicate of alumina and lime with the formulae (Na,Ca)4- 6Al6(Al, Si) 4Si26O72ù24H2O and a relative hardness of 4. It is found in the cavities of basic igneous rocks. Research Heulandite
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Matt and Leela Probert
Abbreviations
Research Acrotomous
