Quartz Rough cut on demand: Amethyst, Citrine, Cognac, rutile quartz, green amethyst, etc.

Rutile Quartz - Golden needles
Rutile Quartz is actually available only in medium quality (slightly included).

About the Quartz family:

The name quartz comes from the German miners' language used during the Middle Age, but its meaning is still not understood.
Quartz is a silicon dioxide and its chemical formula is SiO2. It crystallizes in the trigonal system and has no less than 8 polymorphs (i.e. crystals having the same chemistry but a different internal structure), but, contrary to quartz, are extremely rare and need high temperature and/or pressure condition to be stable. Quartz belongs to the silica group which is a subdivision of the (tecto) silicate class.
Habits are usually a 6-faces prism ended by pyramid but can also be tabular, or show a druse or massive form. Horizontal striae are an important characteristic and are due to the vibration during the crystal growth. It often presents twinning. Crystals are generally important and some pieces bigger than a human-being can be found (Brazil). Quartz has a hardness of 7 on Mohs' scale, where it is a standard-reference and so an important boundary in gemology. In a matter of fact, many of the dust particles in the air are also quartz. So a gem has to be hard enough (i.e. having a hardness equal or higher than 7 to resist abrasion if is daily worn).
Quartz has some attractive properties, which are used by industries as optical lenses, electrical components, for example.
Quartz is, after the feldspar, the most common mineral on the crust part of Earth (13%) and is the principal component of magmatic, metamorphic acid rocks and sandstone.
Quartz is an important family and shows an amazing variety of colors and forms. It is subdivided into 2 categories: macrocrystalline and cryptocrystalline quartz.

Macrocrystalline means "large crystals". Many varieties are well known, popular and show a nice clarity and color.
Amethyst is the violet common-quartz variety used in jewelry owns its color to color centers.
Citrine is the yellow to orange quartz variety. Most of the stones in the market are in fact resulting from the heat treatment of amethysts.
Smoky quartz is the brown variety, rock crystal the colorless.
Quartz is also very rich in inclusions and more than 200 different minerals were identified only in European Alps specimens. Rutilated quartz is may be the most famous and researched: It holds beautiful yellow rutile needles. Aventurine shows aventurescence tue to small reddish platelets of hematites randomly distributed within the stone.
Quartz are also the variety showing phenomena like the chatoyancy in the "tiger's eye" for example. This particular stone is interesting as quartz in fact had replaced a former mineral: crocidolite and as a result has taken its fibrous structure given the special chatoyancy. This phenomena is called pseudomorphism.

Cryptocrystalline (from the Greek word "crypto" meaning "hidden") refers to the crystals which are too small to be seen even through a microscope. They usually react as an aggregate through a polariscope. Crystals from this variety are semitransparent to opaque. Although taken in the large meaning chalcedony is a cryptocrystalline synonymous, stricto sensu chalcedony is the biggest subdivision of this category with many stones as chrysoprase (light green), sard (brownish red) and even fossilized wood (i.e. has been entirely replaced by chalcedony preserving the original shape; it is pseudomorph as "tiger eye"). Another subdivision gathers all kinds of agate (e.g. moss agate, dendritic agate, etc?) while the last one concerns the jasper (e.g. heliotrope).