Quartz

Quartz mineral can be found in abundance in so many locations on Earth, listing them would be impossible. It is a durable, pretty, hard stone, and can be cut or carved in a variety of shapes and sizes. Fairly inexpensive to buy, the deepest colorations are the most valuable. A good quality quartz gemstone is transparent, because light passes directly through the stone, and is free of inclusions, or impurities, with a few notable exceptions.

The two main kinds of quartz have a chemical composition of silicon dioxide. One of these varieties is macrocrystalline quartz, and it can be transparent or translucent. The other main variety is cryptocrystalline quartz and can be translucent or opaque. The crystals in cryptocrystalline quartz are microscopically small and are known as chalcedony.

Some of the different varieties of macrocrystalline quartz and their properties include:

* Amethyst: Amethyst can be the most expensive kind of quartz and ranges in color from a pink-violet to an opaque purple depending on its iron content.

* Citrine: Citrine can be yellow, orange, or gold-brown in color, depending on its iron content. Found in nature, it is usually pale yellow. When commercially heat treated, it takes on a reddish hue.

* Rose Quartz: The titanium in the rare rose quartz gives it a pale or strong shade of pink, which deepens if the crystals are cloudy.

* Tiger's Eye: This gemstone is gold-yellow to gold-brown because of the oxidized iron inclusions. Its name comes from the occurrence of light hitting the stone, making it look like the eye of a tiger.

Some of the different kinds of cryptocrystalline quartz include agates which can be found many different varieties and in multiple colors. Some of the most important trade names of agate gemstones include:

* Dendritic agate: This is a white or colorless stone with markings, called dendrites, resembling ferns or trees.

* Moss agate: Moss agate has green, brown, or red inclusions on a colorless backdrop.

* Scenic agate: Scenic agate has dendrites resembling a brown or reddish landscape.

* Onyx: This stone has two layers, a white top layer and black bottom layer.