Crystal and stones » classification

Hardness of gems and jewels

precious stones — Wed, 16 Sep 2009 13:47:09 +0000

Hardness is perhaps one of the most important features in a stone, especially those of the “gem” series, for no matter how colour, lustre, general beauty and even rarity may entitle a stone to the designation “precious,” unless it possesses great hardness it cannot be used as a gem or jewel.

Consequently, the hardness of [...]

Cleavage of minerals

precious stones — Wed, 16 Sep 2009 12:57:18 +0000

By cleavage is meant the manner in which minerals separate or split off with regularity.

The difference between a break or fracture and a “cleave,” is that the former may be anywhere throughout the substance of the broken body, with an extremely remote chance of another fracture being identical in form, whereas in the [...]

Crystalline structure

precious stones — Wed, 16 Sep 2009 12:51:15 +0000

Before proceeding to the study of precious stones as individual gems, certain physical properties common to all must be discussed, in order to bring the gems into separate classes, not only because of some chemical uniformity, but also because of the unity which exists between their physical formation and properties.

The first consideration, therefore, may [...]