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Ch. 4: Cleavage of Gemstones

Ch. 4: Cleavage of Gemstones Page of 118 Ch. 5: Behavior in Light Text size:minus plus Restore normal size   Mail page  Print this page
CLEAVAGE
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systems, and others show a crystalline structure comprised of several systems. Thus calcspar is in the 2nd, or hexagonal, whilst aragonite is in the 4th, the rhombic, system, yet both are the same substance, viz. :—carbonate of lime. Such a condition is called dimorphism ; those minerals which crystallise in three systems are said to be trimorphous. Those in a number of systems are poly­morphous, and of these sulphur may be taken as an example, since it possesses thirty or more modifications of its crystalline structure, though some authorities eliminate nearly all these, and, since it is most frequently in either the 4th (rhombic) or the 5th (monoclinic) systems, consider it as an example of dimorphism, rather than polymorphism.
These varieties of cleavage affect the character, beauty and usefulness of the stone to a remarkable extent, and at the same time form a means of ready and certain identification and classification.
Ch. 4: Cleavage of Gemstones Page of 118 Ch. 5: Behavior in Light
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