The crystal is transparent quartz crystalloid. To know about the crystal, we need to learn about the mineral of quartz first. Quartz is one of the minerals that distributes widely in the earth’s crust. Its chemical property is silica and the chemical formula is SiO2. The quartz has a large family, which can be divided into three categories: phanerocrystalline, cryptocrystalline and amorphous. The crystal belongs to the category of phanerocrystalline, which means the transparent quartz crystalloid.
The crystal is usually colorless and transparent, but when it contains the impurities of some other metal element (pigment ion), it takes on purple, golden yellow, brown or black and few of them pink. After research, the purple crystal (amethyst) takes on purple mainly because it contains Mn and Fe3+; the pink one is the effect of Mn, Ti ion and hydroxide; the golden yellow one is because of the Fe2+; Some colors are caused by the inclusion impurities of the crystal.
The crystal takes on glass luster, the refractive index is 1.544 – 1.553, the birefringence is 0.009 and the dispersion is 0.013. The amethyst and tawny crystal have polychroism.
The shape of the crystal appears hexagonal, there are usually bands on the cylindrical surface and they can be produced in vug with charming design. There is no cleavage and the fracture is conchoidal. The Mohs hardness is 7, the relative density is 2.56 – 2.66 and it has piezoelectricity. The crystal often contains gas and liquid inclusion. Sometimes there are needlelike mineral (rutile, apyrite, actinolite etc.) inclusions, also with the shining hematite and mica sheet.
The crystal is mainly produced in the geode of pegmatite and quartz vein. The famous crystal origins in the world are Brazil and Madagascar and so on.
The amethyst is the outstanding one amount the numerous crystal members and one of the most valuable one in the quartz family. The ancients think that amethyst can enhance mutual understanding; earn money when doing business; protect the soldiers to win; help the hunters to resist infectious disease and restrain the evil thought. The amethyst is the birthstone of February.
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