BISPHENOIDAL CLASS
(Hemihedral).
Here there are three dyad axes, but no planes of symmetry and no centre of symmetry. The general form {hkl} is a bisphenoid (fig. 61) bounded by four scalene triangles. The other simple forms are geometrically the same as in the holosymmetric class.
Examples: epsomite (Epsom salts, MgSO4.7H20), goslarite (ZnSO4.7H20), silver nitrate, sodium potassium dextrotartrate (seignette salt, NaKC4H4O6.4H20), potassium antimonyl dextrotartrate (tartaremetic, K(SbO)C4H406), and asparagine (C4H8N203'H20).
Hemimorphite.
4. MONOCLINIC 1 SYSTEM
(Oblique; Monosymmetric).
In this system two of the angles between the crystallographic
axes are right angles, but the third angle is oblique, and the axes
are of unequal lengths. The axis which is perpendicular to the other
two is taken as 0Y =b (fig. 62) and is called the orthoaxis or ortho
diagonal. The choice of the other two axes is arbitrary; the vertical
axis (OZ =c) is usually taken parallel to the edges of a prominently
developed prismatic zone, and the clinoaxis or clinodiagonal
(OX =a) parallel to the zoneaxis of some other prominent zone on
the crystal.. The acute angle between the axes OX and OZ is usually
denoted as and it is necessary to know its magnitude, in addition
to the axial ratios a: b: c, before the crystal is completely deter
mined. As in other systems, except the cubic, these elements,
a : b : c and f3, are characteristic of the substance. Thus for gypsum
a : Iz : c=o•6899 : 1:0.4124; 0=80° 42'; for orthoclase a : b : c=
0.6585 : I : O•S554; $=63° 57'; and for canesugar a : b : c=
1.2595 : I : 0.8782; ft =76° 30'.
End of Article: BISPHENOIDAL 

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