The quartz It is the most abundant mineral on the earth's surface. It is composed of silicon dioxide (SiOtwo) generally accompanied by impurities in trace amounts. It can be found as part of numerous types of rocks or as mineral crystals. Rock crystal is the name by which the highest purity variety of quartzthe variety that is composed almost entirely of silicon dioxide.
There are numerous varieties of quartz depending on the trace elements present. For example, amethyst is quartz with iron impurities; and rose quartz is formed by quartz with impurities of dumortierite, an aluminum boron-silicate mineral.
Rock crystal is practically pure silicon dioxide with hardly any impurities affecting its color, resulting in a completely crystalline mineral. transparent, colorless and without color defects.
Rock crystal has been widely used as a gem or precious stone due to its appearance and low cost, even as a diamond imitation, although due to its characteristics it cannot be considered a precious stone as such.
Rock crystal, and quartz in general, has numerous industrial and technological applications. They are used to make glass, in optical components, and as a semiconductor element in electronics devicesprocessors and microchips.
Outstanding chemical characteristics
The composition of quartz (silicon oxide) places it in the class 4 of the Strunz classification together with the other minerals composed of oxides or hydroxides. Specifically, quartz belongs to group 4.DA.
Quartz can contain impurities of lithium, sodium, potassium, iron or titanium, according to which the different quartz varieties appear, rock crystal being the variety with the lowest impurity content.
It has a hardness of grade 7 on the Mohs scale, which means that it can be scratched by glass and most common metals. It's a mineral considered brittle which can be conchoidally broken.
At the molecular level, quartz can adopt two structures, the quartz-α (alpha) and quartz-β (beta). Alpha quartz is also known as base quartz and crystallizes in the trigonal system. Low quartz exists at temperatures below 573 ºC. Beta quartz, or high quartz, appears between 573 – 867 ºC and crystallizes in the hexagon system. Above 876 ºC it transforms into tridymite.
The ideal crystalline form of rock crystal is a six-sided prism ending at each end with a six-sided pyramid.
Gallery
A very important characteristic of quartz and rock crystal is the piezoelectricity and pyroelectricity. Thanks to piezoelectricity, quartz crystals acquire electrical polarization when they are subjected to mechanical stresses, for example compression. Pyroelectricity also generates electrical polarization of the crystal in response to changes in temperature.
Both properties make quartz a material semiconductor, since it can act as an insulator or as a conductor depending on the conditions applied. Thanks to this property, quartz has numerous industrial applications and is essential in many electronic devices.
Most quartz is formed from siliceous rock magma, although it can also form at hydrothermal vents. Crystals with good crystallization conditions can reach several meters and weigh hundreds of kilos, but the highest purity rock crystal is not very common, in fact the rock crystal usually used for glass or jewelry is low cost compared to the cost of quartz with the level of purity required by the electronics industry.