Hexagonal mineral system

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

White powder. M.p. 1650°C (appreciable volatilization) distills without decomposition at high vacuum (5 lO " mm.), d 4.14. Solubility (18°C) 0.688 mg. (freshly precipitated)/100 ml. H3O. Soluble in dilute mineral acids. Hardness 3.5-4 (both modifications). The low-temperature modification (sphalerite) crystallizes in the cubic B3 system (zincblende), the high-temperature modification (wurtzite) in the hexagonal b4 system. Transition point about 900 °C. Grinding at room temperature converts the metastable wurtzite to zincblende. 

As an example of isomorphism we may consider the minerals rhodo-chrosite, MnCOa, and calcite, CaCOa. Crystals of these two substances resemble one another closely, as shown in Figure 4-4. They both belong to the hexagonal crystal system (Section 2-5), and they both have... 

The Swedish mineral finnemanite 4 contains lead orthoarsenite in combination with lead chloride, the composition being 3Pb3(As03)2. PbC l2 (see p. 15). It occurs in dark grey or black prismatic crystals belonging to the hexagonal system and of axial ratio a c = 1 0-6880. 

ALUNITE. The mineral alunite, KAl3(S04)2(0H)t , is a basic hydrous sulfate of aluminum and potassium a variety called natroalunite is rich in soda. Alunite crystallizes in the hexagonal system and forms rhombohedrons with small angles, hence resembling cubes. It may be in fibrous or tabular forms, or massive. Hardness, 3.5-4 sp gr, 2.58-2.75 luster, vitreous to pearly streak white transparent to opaque brittle color, white to grayish or reddish,... 

NICKELINE. A nickel arsenide mineral, NiAs, crystallizes in the hexagonal system but is usually found massive. Color, light copper hardness, 5.0-5.5 specific gravity, 7.784 luster, metallic opaque. Found in several European localities and in the Province of Ontario, Canada in die United States at Franklin, New Jersey, and Silver Cliff, Colorado. It is an ore of nickel. 

PROUSTITE. This ruby-silver mineral crystallizes in the hexagonal system its name is a product of its scarlet-to-vermilion color when first mined It is a silver arsenic sulfide. AgjAsS, of adamantine luster Hardness of 2-2,5 specific gravity of 5.55-5.64. Usual crystal habit is prismatic to rhombohedral more commonly occurs massive. Conchoidal to uneven fracture transparent to translucent color, scarlet to vermilion red. Light sensitive must be kept in dark environment to maintain its primary character. A product of low-tcmpcraturc formation in most silver deposits. Notable world occurrences include the Czech Republic and Slovakia, Saxony, Chile and Mexico. Found in minor quantities in the United States the most exceptional occurrence at the Poorman Mine, Silver City District. Idaho where a crystalline mass of some 500 pounds (227 kilograms) was recovered m 1865, It was named for the famous French chemist, Louis Joseph Proust. 

VANADINITE. The mineral vanadimte corresponds to the formula Pb VO Cl, being composed of lead chloride and lead vanadate in the proportion of 90.2% of the former and 9.8% of the latter. It crystallizes in the hexagonal system, is usually prismatic, but the ciystals are often skeletal or cavernous it may be found in crusts. Its fracture is uneven brittle hardness. 2.75-3 specific gravity. 6.86 fresh fractures show a resinous luster color, yellow, yellowish-brown, reddish-brown, and red streak, white to yellowish translucent to opaque. Vanadinite, not a common mineral, occurs as an alteration product in lead deposits. It is found in the Ural Mountains, Austria, Spain, Scotland, Morocco, the Transvaal, Argentina, and Mexico, In the United States it occurs in Arizona, New Mexico, and South Dakota, It is used as an ore of vanadium and to some extent of lead as well. It is interesting to note that this mineral was first described as a chromate upon its discovery in Mexico in 1801, It was not until the discovery of the element vanadium in 1830 that the true nature of this compound was known. 

WURTZITE. A mineral zinc sulfide, (Zn, Fe),S. similar to sphalerite. Crystallizes in the hexagonal system. Hardness, 3.5-4 specific gravity, 3.98 color, brownish-black with resinous luster. Named after Adolphe Wiirtz. Fiance. 

In Fig. 30, a three-dimensional model is presented in which only the organic phases are shown. Hexagonal plates of MM alternate with pleated sheets of CP. The hydrophobic sides of MM are facing each other and encase the mineral phase. The relationship between hydrophobic bonding and accessible surface area in proteins, and the effect of polar and non-polar side groups on free energy values has recently been discussed246. For informations on hydrophobicity in protein systems see Refs.247-252. ... 

Minerals of the hexagonal system, such as quartz, are referrable to four crystallographic axes. Three axes, a, a2 and lie in a horizontal plane and have equal atomic spacing with angles of 120° between the positive ends. The fourth axis, c, is vertical and at right angles to the plane of ai, a2, and 83 with a different atomic spacing. 

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. 

Ferrous sulphide, FeS, occurs in nature as the mineral troilite (see p. 23), which is found in nodules in the majority of meteorites containing iron. When crystalline it appears to belong to the hexagonal system, and has probably been formed in the presence of excess of iron.8 It may be obtained by the direct union of iron and sulphur at red heat. If the iron is m the form of filings and is intimately mixed with the sulphur, the mass becomes incandescent when once the reaction has been started. Synthetic iron disulphide, heated above 700° C., is converted into ferrous sulphide.9... 

Ferrous carbonate, FeC03, occurs in nature as spathic iron ore (see p. 20), which, however, is not pure, even m the crystalline form, as it contains several other isomorphous carbonates. When crystalline, the mineral is generally known as chalybite or siderite. The crystals belong to the hexagonal system, and are brown in colour. Upon exposure to moisture and air they are gradually converted into hydrated ferric oxide. When heated, they begin to decompose at about 400° C.4 in air. 

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