The name "quartz" comes from the German "Quarz", which is of Slavic origin (Czech miners called it křem). Other sources insist the name is from the Saxon word "Querkluftertz", meaning cross-vein ore.  (From Wikipedia, the free encyclopedia)

Quartz crystals have been used to make oscillators for radios, computer chips, and clocks.

Chemistry: SiO2 , Silicon 
Class: Silicates
Hardness is 7
Density is 2.65 g/cm³
The typical shape is a six-sided prism that ends in six-sided pyramids
A quartz geode consists of a hollow rock (usually with an approximately spherical shape) with a core lined with a bed of crystals.
 
 
Other varieties are Amethyst, Citrine, Rose Quartz, and Smoky Quartz.
Quartz is the most common mineral on Earth.  

Amethyst is a purple color.
Citrine is a yellow to orange. Although citrine occurs naturally, the majority is the result of heat-treated amethyst.   
Rose quartz is rosy pink to redish.
Smoky quartz is gray to brownish.

A quartz arrowhead that is estimated to be over 11,000 years old was discovered at the Mount Blakely Dam site in Garland County. Before AD 1000, the Plum Bayou people built the Toltec Mounds in the Arkansas River Valley. They made arrowheads, scrapers, and knives out of clear quartz. The quartz was more difficult to work with than other available stones and may have served a ritual purpose. In 1541, Spanish explorers led by Hernando de Soto found that the Indians in the region that is now Arkansas were making arrowheads out of quartz crystal. Archaeologists have yet to discover prehistoric quartz mines, leading many to believe that the quartz used by these Indians was found on the surface. The Hunter-Dunbar journals (circa 1804) make reference to quartz crystals and other minerals from the Little Missouri River valley in what was certainly the Ouachita Mountains.

In mineralogy, an inclusion is any material that is trapped inside a mineral during its formation.

According to Hutton's law of inclusions fragments included in a host rock are older than the host rock itself.

Inclusions are usually other minerals or rocks, but may also be water, gas or petroleum. Liquid or vapor inclusions are known as fluid inclusions. In the case of amber it is possible to find insects and plants as inclusions.