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Quartz is a crystalline form of silicon diode, SiO2. The name Quartz is derived from the German word ‘quaz’, although others believe the word's origin is from the Saxon word Querkluftertz, meaning cross-vein ore.
Quartz is widely used within electronics where quartz resonators are used as high performance resonators for use in filters and oscillators.
The are several interesting properties that can be attributed to quartz:
- Piezo-electric properties: Quartz exhibits the peizo-electric effect. In this if a strain is placed onto the crystal, then an electro-motive force is produced and this can be detected by placing electrodes on its surface.
- Melting point: The melting point for quartz is above 1700°C.
- Curie temperature - alpha and beta quartz: The Curie temperature for quartz is 573°C. Below this temperature the form exits and it has its piezo-electric properties. Above 573°C most of its piezo electric properties are lost and t is referred to as beta quartz.
Production of quartz
Quartz occurs naturally with the main sources of crystalline quartz being found in Brazil. Here crystals of many shapes and sizes were found.
With its widespread update within the electronics industry supplies started to become exhausted by the 1940s and 1950s.
The diminishing supply lead to the development of manufacturing methods to create synthetic quartz.
The process for manufacturing synthetic quartz entails dissolving raw silicon diode, SiO2 in an alkali water solution at around 400°C and under high pressure.
The crystals can then be grown. This is a very slow process and often growth rates are as little as 1mm per day. However this slow rate provides high purity and generally high quality crystals . The quality is as good as that found naturally.
Having control of the growth enables the crystals to be grown to meet the requirements of the crystal manufacturers. It enables different dimensions and orientations to be produced.
Quartz crystal properties
There are several key properties that quartz crystals possess which are of use:
- Crystal shape: Both natural and synthetic quartz crystals have a hexagonal cross section with the ends having six sided pyramid shapes. The directions within the crystals are of major importance for resonator manufacture and they are identified as X, Y and Z axes. The Z axis runs longitudinally between the ends through the centre of the crystal, and the direction of greatest electrical sensitivity is identified as the X axis. The Y axis joins two opposite faces. As there are six faces to the crystal there are three X and Y axes.
- Left and right handed quartz: Quartz is termed enantiomorphous. This means that it has both left and right handed versions. This difference appears in the optical rotation, although other properties between the two versions are identical. Generally right handed quartz crystals are used for resonator manufacture.
- Quartz is anisotropic: Many of the properties of quartz depend upon the orientation of the quartz bar, and more importantly the lattice within the crystal. In terms of its use within quartz crystal resonators, one of the important aspects that is sensitive to its direction is the peizo electric effect. As a result the direction in which the individual quartz crystal blanks are cut determines many of their properties. Different vibration modes are excited by electrical impulses dependent upon the direction of the cut.
Forms of quartz crystal
There are many forms of quartz that exist apart from the crystals used for electronics resonators. Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar.
|Rock crystal||Colourless & clear|
|Amethyst||Purple and transparent|
|Rose quartz||Pink and transparent|
|Carnelian||Reddish orange and translucent|
|Agate||Multicoloured and semi translucent|
|Onyx||A form of agate where the bands are straight|
|Jasper||Red to brown and opaque|
|Citrine||Yellow through reddish orange to brown and transparent|
|Prasiolite||Mint green and transparent|