Tetragonal mineral system

There are six mineral systems Isometric, Hexagonal, Tetragonal, Orthorhombic, Monoclinic, and Triclinic. The Trigonal... 

Tellurium dioxide is known in two different crystalline forms. Crystals of the tetragonal system,2 but almost regular (a c — 1 1-1076), of density 5-66, are obtainable from the solution in nitric acid, while the molten dioxide when slowly cooled deposits rhombic needles 3 (a b c=0 4566 1 0-4693) of density 5-93 and identical with the rarely occurring mineral tellurite. 

ANATASE. The mineral anatase, TiC>2 crystallizing in the tetragonal system is a relatively uncommon mineral. It occurs as a tri-morphous form of Ti02 with rutile mid brookite. Rutile and anatase have tetragonal crystallization brookite, orthorhombic. Hardness, 5.5-6 sp. gr. 3.82-3.97 brittle with sub-conchoidal fracture color, shades of brown, into deep blue to black also colorless, grayish, and greenish also transparent to opaque with adamantine luster. 

AUTUNITE. This mineral is a hydrous phosphate of calcium and uranium, crystallizing in the tetragonal system, usually in thin tabular crystals. Good basal cleavage hardness. 2-2.5 specific gravity, 3.1 luster, subadamantine to pearly on the base color, lemon yellow streak, yellow transparent to translucent strongly fluorescent. 

Minerals of the tetragonal system are referrable to three crystallographic axes that make right angles with each other. The two horizontal axes aj and a2 have equal atomic spacing but the vertical axis c has an atomic spacing that is not equal to aj or... 

Polarized light having a vibration direction parallel to the plane of aj and a2 in minerals of the tetragonal system or parallel to the plane of ai, a2 and 83 in minerals of the hexagonal sys tern will be spoken of as the ordinary ray. This n is omega. 

If optical examination shows two n s, the two indices will be omega and epsilon or e1, and the mineral belongs to either the hexagonal or the tetragonal system. Caution In some minerals, one n may be so close to another n that it may be falsely assumed that there are only two n s. Minerals of the tetragonal or hexagonal systems are uniaxial. 

Zirconia is an important refractory ceramic. It also forms the basis of solid electrolytes in systems such as Zr02-Y203. Both zirconia and hafnia figure prominently in refractory ceramics proposed for the containment of uranium and plutonium radioactive waste. The monoclinic form of Zr02, baddeleyite, is a widespread accessory mineral. Zirconia undergoes transitions from monoclinic to tetragonal to cubic, with thermochemical parameters listed in Table 5. 

Careful measurement of mineral specimens allowed crystals to be classified in terms of six crystal families, called anorthic, monoclinic, orthorhombic, tetragonal, hexagonal and isometric. This classification has been expanded slightly by crystallographers into seven crystal systems. The crystal systems are sets of reference axes, which have a direction as well as a magnitude, and hence are vectors1. The crystal families and classes are given in Table 1.1. 

Formula Chemical class Chemical type Pb,(C03)Ci, Anhydrous carbonate with hydroxyl or halogen (AB),(X03>Z, Crystal system Mineral group Space group Tetragonal Phosgenite P4/mbm... 

Lead tunstate, PbW04, appears to have had limited use in its synthetic form as a pigment. There are also two lead tungstate minerals, the tetragonal stolzite and monoclinic raspite qq.v. both PbW04) however it is not known what crystal system the synthetic pigment takes. 

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