Pinacoids

I) as pale-yellow crysts and 2) as color tablets both belonging to the pinacoidal class of the tri-clinic system mp, loses its water at 120—130° and explds at 240° Easily sol in w, diff sol in aq ale, insol in abs ale and other org solvents It was first prepd by Palazzo as a by-product in the prepn of 1-hydroxytetrazole from hydrazoic... 

Data obtained from photographs of the if-radiation of molybdenum reflected from the ground pinacoids of a brookite crystal (variety arkan-site from Magnet Cove, Ark.)3) are given in Table I. These lead to a unit with = 2,291 A, [Pg.485]

The older data as to the crystallography of the trisaccharide melezitose are not only incomplete but contradictory. Villiers described it as monoclinic, bounded by a prism, m, the base p, and the side pinacoid he obtained the angles g1-.m = 136° 38 and m p = 92° 40. On the other hand Alekhine8 found it to be rhombic, his crystals showing front and side pinacoids, o and a, prism, m, and front and side domes, od and ga, although he recorded no measurements at all. In both cases the dihydrate is supposed to have been represented, but no information has been available to indicate whether this was a case of dimorphism or whether the two authors were in fact not dealing with the same substance. 

Forms are frequently denoted by letters. By convention, the pinacoids that cut the a-, b- and c-axes are referred to as the a, b and c forms, respectively, and the 111 and 101 forms are p and m, respectively. In most other cases, the lettering is arbitrary having been chosen by the person who first described the crystal. The angles between the different faces will, however, remain constant and this assists in assigning a crystal to its symmetry class (Tab. 4.1). Because of the arbitrariness of the lettering it will not be used in this book. 

TOPAZ. The mineral topaz is a silicate of aluminum and fluonne corresponding to the formula A SiO F, OTT)2. It is orthorhombic and its crystals are mostly prismatic terminated by pyramidal and odier faces, the basal pinacoid being often present, Massive varieties are known. It has an easy and perfect basal cleavage, hence for this reason gems or fine specimens should be handled with care to avoid developing cleavage... 

Crystal System Triclinic Form and Habit Plates flattened parallel to and usually lying on 001, showing the pinacoids, jooij-, joioj, lOO, and occasionally the prisms, JllOj-... 

E, 254, C2 Tetragonal disphenoid, tetragonal prism, pinacoid Ca2B(0H)4As04... 

Aim E, 2C4, C2, i, 25 4, Tetragonal dipyramid, tetragonal prism, pinacoid PbMo04... 

Ditetragonal dipyramid, tetragonal dipyramid, ditetragonal prism, tetragonal prism, pinacoid Rutile... 

Trigonal trapezohedron, rhombohedron, trigonal dipyramid, ditrigonal prism, hexagonal prism, trigonal prism, pinacoid Low quartz... 

Hexagonal scalenohedron, rhombohedron, hexagonal dipyramid, dihexagonal prism, hexagonal prism, pinacoid Comndum... 

Trigonal dipyramid, trigonal prism, pinacoid None... 

Hexagonal dipyramid, hexagonal prism, pinacoid Apatite... 

E,C2 Monoclinic Sphenoid, pedion, pinacoid FeAl2(S04>4 22H2O... 

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