Quartz is the second most abundant mineral in the Earth's continental crust.
It is made up of a continuous framework of SiO4 silicon–oxygentetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz, several of which are semi-precious gemstones, including Onyx, Amethyst and Tigers eye.
Colours
The pretty crystals and vivid colors you'll see in jewelry and in rock shops are scarce. Here are some of those precious varieties:
- Clear, colorless quartz is called rock crystal.
- Translucent white quartz is called milky quartz.
- Milky pink quartz is called rose quartz. Its color is thought to be due to various impurities (titanium, iron, manganese) or microscopic inclusions of other minerals.
- Purple quartz is called amethyst. Its color is due to "holes" of missing electrons in the crystal in combination with iron impurities.
- Yellow quartz is called citrine. Its color is due to iron impurities.
- Green quartz is called prasiolite. Iron impurities account for its color, too.
- Gray quartz is called smoky quartz. Its color is due to "holes" of missing electrons in combination with aluminum impurities.
- Brown smoky quartz is called cairngorm and black smoky quartz is called morion.
Occurrence
Quartz is an essential constituent of granite and other felsic igneous rocks. It is very common in sedimentary such as sandstone and shale and is also present in variable amounts as an accessory mineral in most carbonate rocks. It is also a common constituent of schist, gneiss, quartzite and other metamorphic rocks. Because of its resistance to weathering it is very common in stream sediments and in residual soils.
While the majority of quartz crystallizes from molten magma, much quartz also chemically precipitates from hot hydrothermal veins as gangue, sometimes with ore minerals like gold, silver and copper. Large crystals of quartz are found in magmatic pegmatites. Well-formed crystals may reach several meters in length and weigh hundreds of kilograms.
Naturally occurring quartz crystals of extremely high purity, necessary for the crucibles and other equipment used for growing silicon wafers in the semiconductor industry, are expensive and rare.
Now for the easy part the questions.
At the listed co-ordinates you should find a quartz vein running through the rock under your feet.
- How long is the visable part of the vein?
- What colour is the vein? And what causes it to be this colour?
References
- http://en.wikipedia.org/wiki/Quartz
- http://www.quartzpage.de/gen_form.html
- http://www.ehow.com/how-does_4924493_how-quartz-formed.html