Crystal and stones » cleavage

Tourmaline

precious stones — Wed, 16 Sep 2009 16:04:44 +0000

The tourmaline is a most complex substance; almost every stone obtained has a different composition, some varying but slightly, with mere traces of certain constituents which other stones possess in a perceptible degree.

Consequently, it is not possible to give the chemical formula, which might, and possibly would, be found but seldom, even in [...]

Beryl

precious stones — Wed, 16 Sep 2009 15:59:43 +0000

The beryl is a compound of silicates of beryllia and alumina, with the formula 3BeOSiO2 + Al2O3,3SiO2, or 3BeO,Al2O3,6SiO2. It differs very little indeed from the emerald, with the exception of its colour.

In the ordinary varieties this is somewhat poor, being mostly blue, or a dirty or a greenish yellow; the better kinds, [...]

Topaz

precious stones — Wed, 16 Sep 2009 15:57:38 +0000

The name topaz is derived from the Greek topazos, which is the name of a small island situated in the Gulf of Arabia, from whence the Romans obtained a mineral which they called topazos and topazion, which mineral to-day is termed chrysolite.

The mineral topaz is found in Cornwall and in the British Isles [...]

Corundum

precious stones — Wed, 16 Sep 2009 15:42:03 +0000

This mineral is a species of crystal, or crystalline alumina -an almost pure anhydrous alumina, Al2O3 -in many varieties, both of shape and colour.

The chief stone is the ruby, considered, when large, to be of even more importance and value than the diamond. There are many other red stones in this group; sapphires, [...]

Testing precious stones

precious stones — Wed, 16 Sep 2009 14:53:23 +0000

We now arrive at the point where it is necessary to discuss the manufacture and re-formation of precious stones, and also to consider a few of the tests which may be applied to all stones. These are given here in order to save needless repetition; the tests which are specially applicable to individual stones will [...]

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 [...]