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Crystals are grouped into seven systems. Triclinic crystals, which have only a center of symmetry or are completely asymmetrical; forms most common are the pinacoid and pedion. Examples include albite and other plagioclase feldspars, turquoise, rhodonite, and kyanite.

Monoclinic crystals are symmetrical within one plane of symmetry or about one twofold axis or both. Forms commonly seen are the prism, pinacoid, dome, sphenoid, and pedion. Examples include azurite, brazilianite, euclase, jadeite, nephrite, lazulite, serpentine, spodumene, and titanite.

The Orthorhombic crystals have three planes of symmetry and commonly seen forms are the rhombic pyramid, bisphenoid, dome, pinacoid, and pedion. Examples include andalusite, chrysoberyl, iolite, topaz, peridot, marcasite, danburite, prehnite, staurolite, variscite, and zoisite (tanzanite).

Tetragonal crystals possess one fourfold axis of symmetry. Most common forms are the 16 faced bipyramid, tetragonal bipyramid (8 faces), ditetragonal prism, tetragonal prism and basal pinacoid. Examples include cassiterite, rutile, vesuvianite, wardite, and zircon.

Trigonal or rhombohedral crystals have four crystallographic axes. The commonest form is the rhombohedron which looks like a cube compressed along one of the diagonal threefold axes. Other forms commonly see are the prism, pyramid, bipyramid, trigonal trapezohedron, ditrigonal scalenohedron (12 faces), basal pinacoid, and an occassional pedion. Examples include calcite, corrundum (rubies and sapphires), dioptase, hematite, quartz, phenakite, rhodochrosite, smithsonite, and tourmaline.

Hexagonal crystals have a sixfold axes of symmetry with four crystallographic, three of which are the same length. Commonest forms are hexagonal and dihexagonal prisms, pyramids, bipyramids, hexagoanl trapezohedron, basal pinacoid and occassionally the pedion. Examples are apatite, beryl (emerald, morganite, aquamarine, goshenite, heliodor), and zincite.

Finally, the cubic or isometric crystals have four characteristic threefold axes of symmetry. Most commonly seen are the cube, octohedron, rhombic dodecahedron, cubic trapezohedron, trisoctahedron, tetrahexahedron, and hexoctahedron. Examples include cuprite, diamond, flourite, garnet, lazurite, sphalerite, and spinel.

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