Online Encyclopedia


Online Encyclopedia
Originally appearing in Volume V07, Page 581 of the 1911 Encyclopedia Britannica.
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TRIGONAL PYRAMIDAL CLASS (Hemimorphic-tetartohedral). Here there is only the triad axis of symmetry, which is uniterminal. The general form {hkl} is a trigonal pyramid consisting of three faces at one end of the crystal. All other forms, in which the faces are neither parallel nor perpendicular to the triad axis, are trigonal pyramids. All the prisms are trigonal prisms; and perpendicular to these are two pedions. The only substance known to crystallize in this class is sodium periodate (NaI04.3H20), the crystals of which are circularly polarizing.
End of Article: TRIGONAL PYRAMIDAL CLASS (Hemimorphic-tetartohedral)
TRIGONOMETRY (from Gr. rpiywvov, a triangle, /ATpov...

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