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Each crystallographic point group defines the (geometric) crystal class of the crystal. The point group of a crystal determines, among other things, the directional variation of physical properties that arise from its structure, including optical properties such as birefringency , or electro-optical features such as the Pockels effect .
Pyromorphite is a mineral species composed of lead chlorophosphate: Pb 5 (P O 4) 3 Cl, sometimes occurring in sufficient abundance to be mined as an ore of lead. [5] Crystals are common, and have the form of a hexagonal prism terminated by the basal planes, sometimes combined with narrow faces of a hexagonal pyramid. [6]
Crystal healing is a pseudoscientific alternative-medicine practice that uses semiprecious stones and crystals such as quartz, agate, amethyst or opal. Despite the common use of the term "crystal", many popular stones used in crystal healing, such as obsidian, are not technically crystals. Adherents of the practice claim that these have healing ...
Tetrahedrite gets its name from the distinctive tetrahedron shaped cubic crystals. The mineral usually occurs in massive form, it is a steel gray to black metallic mineral with Mohs hardness of 3.5 to 4 and specific gravity of 4.6 to 5.2.
identifying important raw materials and minerals as well as their names and chemical formulae. describing the crystal structure of important materials and determining their atomic details; learning the systematics of crystal and glass chemistry. understanding how physical and chemical properties are related to crystal structure and microstructure.
Euhedral pyrite crystals A subhedral sample showing sharp to anhedral pyrargyrite crystals. Euhedral and anhedral are terms used to describe opposite properties in the formation of crystals . Euhedral (also known as idiomorphic or automorphic ) crystals are those that are well-formed, with sharp, easily recognised faces .
Hemimorphite "spray" of crystals from Durango, Mexico (size: 2.9 × 2.1 × 2.0 cm). Hemimorphite most frequently occurs as the product of the oxidation of the upper parts of sphalerite bearing ore bodies, accompanied by other secondary minerals which form the so-called iron cap or gossan.
Well-developed crystals are found in the emery deposits of the Ural Mountains and at Chester, Massachusetts, and in kaolin at Schemnitz in Hungary. If obtainable in large quantity, it would be of economic importance as a source of aluminium. [5] Diaspore, along with gibbsite and boehmite, is a major component of the aluminium ore bauxite. [3]