Crystal and stones » opal

Birthstone

precious stones — Fri, 18 Sep 2009 14:23:24 +0000

Birthstones have their roots in ancient astrology, and there have been many birthstone lists used over the years. The most common one today is based on a list first publicized by the U.S. jewelry industry in the 1950s.

This list assign birthstones as follows:

* January – Garnet * February – Amethyst * [...]

Chrysoberyl

precious stones — Wed, 16 Sep 2009 15:54:00 +0000

There are certain stones and other minerals which, owing to their possession of numerous microscopically fine cavities, of a globular or tubular shape, have the appearance of “rays” or “stars,” and these are called “asteriated.”

Several of such stones have been discussed already in the last chapter, and in addition to these star-like rays, [...]

Red and rose gemstones

precious stones — Wed, 16 Sep 2009 15:11:03 +0000

Red and rose gemstones

Hardness. Specific Gravity.

Carnelian (a variety of Chalcedony) 6-1/2 2.598-2.610 Diamond 10 3.502-3.564 Deep Red Garnet 7-1/4 3.40-4.50 Jasper 7 2.668 Opal (the “Fire Opal”) 5-1/2-6-1/2 2.21 Ruby 9 4.073-4.080 Rhodonite 5-1/2-6-1/2 3.413-3.617 Sapphire 9 4.049-4.060 Spinel Ruby 8 3.614-3.654 Topaz 8 3.500-3.520 Tourmaline 7-1/4 3.024 Zircon 7-1/2 4.70-4.88

White or colourless stones

precious stones — Wed, 16 Sep 2009 14:58:08 +0000

White or colourless stones

Hardness. Specific Gravity.

Beryl 7-3/4 2.709-2.81 Corundum 9 3.90-4.16 Diamond 10 3.502-3.564 Jade 7 3.300-3.381 Opal 5-1/2-6-1/2 2.160-2.283 Phenakite 7-3/4 2.965 Quartz 7 2.670 Rock-crystal 7 2.521-2.795 Sapphire 9 4.049-4.060 Spinel 8 3.614-3.654 Topaz 8 3.500-3.520 Tourmaline 7-1/4 3.029 Zircon 7-1/2 4.700-4.880

Heat-rays to precious stones

precious stones — Wed, 16 Sep 2009 14:30:16 +0000

Another method of isolating certain stones is by the action of heat-rays.

Remembering our lessons in physics we recall that just as light-rays may be refracted, absorbed, or reflected, according to the media through which they are caused to pass, so do heat-rays possess similar properties.

Therefore, if heat-rays are projected through precious [...]

Hauynite to Opal

precious stones — Wed, 16 Sep 2009 14:18:50 +0000

Group F. -Stones whose specific gravity lies between 2.00 and under 2.50.

Hauynite 2.470 and occasionally to 2.491 Lapis lazuli 2.461 Moldavite 2.354 Opal 2.160 and according to variety to 2.283 Opal (Fire Opal) 2.210 (average)

Specific gravity of gemstones

precious stones — Wed, 16 Sep 2009 13:53:09 +0000

The fixing of the specific gravity of a stone also determines its group position with regard to weight; its colour and other characteristics defining the actual stone.

This is a safe and very common method of proving a stone, since its specific gravity does not vary more than a point or so in different [...]

Pleochroism and colour of minerals

precious stones — Wed, 16 Sep 2009 13:13:11 +0000

Color is one of the most wonderful effects in nature. It is an attribute of light and is not a part of the object which appears to be coloured; though all objects, by their chemical or physical composition, determine the number and variety of vibrations passed on or returned to the eye, thus fixing their [...]

Precious stones

precious stones — Wed, 16 Sep 2009 11:09:08 +0000

What constitutes a precious stone is the question which, at the onset, rises in the mind, and this question, simple as it seems, is one by no means easy to answer, since what may be considered precious at one time, may cease to be so at another.

There are, however, certain minerals which possess distinctive [...]