Monoclinic mineral system

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

Pressure-induced phase transitions in the titanium dioxide system provide an understanding of crystal structure and mineral stability in planets interior and thus are of major geophysical interest. Moderate pressures transform either of the three stable polymorphs into the a-Pb02 (columbite)-type structure, while further pressure increase creates the monoclinic baddeleyite-type structure. Recent high-pressure studies indicate that columbite can be formed only within a limited range of pressures/temperatures, although it is a metastable phase that can be preserved unchanged for years after pressure release Combined Raman spectroscopy and X-ray diffraction studies 6-8,10 ave established that rutile transforms to columbite structure at 10 GPa, while anatase and brookite transform to columbite at approximately 4-5 GPa. 

AZURITE. This mineral is a basic carbonate of copper, crystallizing in the monoclinic system, with the formula Cu2.(C03)2(0H)2, so called from its beautiful azure-blue color. It is a brittle mineral with a conchoidal fracture hardness. 3.5-4 sp gr, 3.773 luster, vitreous, color and streak, blue transparent to translucent Azurite, like malachite, is a secondary mineral, but for less common than malachite. It is formed by the action of carbonated waters on compounds of copper or solutions of copper compounds. 

BARYTOCALCITE. This mineral is a carbonate of barium and calcium il crystallizes in the monoclinic system but occurs massive as well. Il lias a perfect cleavage parallel to the prism and one, less perfect, parallel to the base fracture, sub-conchoidal brittle hardness, 4 specific gravity, 3.66-3.71 luster, vitreous color, white or gray or may be greenish or yellowish transparent to translucent. Barytocalcite is found in Cumberland. England, associated with barite and fluorite. 

BORAX. This hydrated sodium borate mineral, NaiBtOy 101 1, O, is a product of evaporation from shallow lakes and plays. Borax crystallizes in the monoclinic system, usually in short prismatic crystals. Its color grades from colorless through gray, blue to greenish. Vitreous to resinous luster of translucent to opaque character. Hardness of 2-2.5, and specific gravity of 1.715. 

BOULANGERITE. A mineral compound of lead-antimony sulfide, PbjSb Sn. Crystallizes in the monoclinic system hardness, 2.5-3 specific gravity, 6.23 color, lead gray. 

BROCHANTITE. A mineral composed of basic copper sulfate corresponding to the formula Cut (S04)(OH)/, crystallizing in the monoclinic system in needle-like prisms, or forming druses or masses. Hardness, 3.5-4 specific gravity, 3.9 vitreous luster color, green streak, green transparent to translucent. 

GEOCRON ITE. A mineral sullide of lead, antimony and arsenic. Phs-ShAsS. Crystallizes in the monoclinic system. Hardness, 2.5 specific gravity. 6 4 color, gray to blue with metallic luster opaque. 

HESSITE. A mineral telluride of silver. AgyTe. with some gold, crystallizing in the monoclinic syslem at normal temperatures isometric system above I49.5F (65.3 C). Crystalline form not ohvious at normal temperatures. Hardness. 2-3 specific gravity. 8.24-8.45 color, gray with metallic luster opaque. Named after G.H. Hess (1802— 1850). 

POLYBASITE. A mineral antimony sulfide of silver (Ag.C n)t. Sb,S. in which copper substitutes for silver to approximately 30 atomic percent. It crystallizes in the monoclinic system hardness, 2-3 specific gravity, 6.3 color, black, dark ruby red in thin splinters with metallic luster nearly opaque. From the Greek, meaning many, suggesting the many-metal basis. 

Six types of spectra are theoretically possible in minerals of the orthorhombic, monoclinic and triclinic systems (McClure, 1959). However, for electric dipole transitions only three spectra are usually distinguished. These are the a, P and y spectra obtained when light is polarized along each of the three indicatrix axes, which in orthorhombic minerals such as olivine and orthopyroxene correspond to the three crystallographic axes. The majority of the spectra of minerals described in chapters 4 and 5 consist of polarized spectra measured in the three mutually perpendicular directions corresponding to a, P and y polarized light... 

The pyroxenes are the most abundant minerals, after olivine, in perido-tites, which are the dominant constituents of the upper mantle. It is not surprising, therefore, that there has been considerable interest in the mechanical properties of the pyroxenes, and a review has recently been given by Doukhan et al. (1986). The orthorhombic pyroxenes deform by slip and by a shear transformation that produces monoclinic lamellae (one or a few unit cells thick) parallel to (100). Coe and Kirby (1975) and McLaren and Etheridge (1976) have shown that the shear transformation is achieved by the glide of partial dislocations of b = 0.83[001] in (100), which leave partial dislocations of b = 0.17[001] terminating the shear lamellae. The dominant slip system is (100) [001]. Recent TEM observations by van Duysen, Doukhan, and Doukhan (1985) suggest that the dislocations associated with this slip system may be dissociated into four partials and that the slip system (100) [010] may also be activated. These observations are discussed in Section 9.9.1. 

---