AUSSIE AMETHYST CRYSTAL
A great Aussie Amethyst Crystal. Good natural point and some iron staining around the base of crystal. Just as it was when it came out of the ground. Australian Amethyst is not all that common, and many people do like to have a piece from here. This piece has a great termination and fits well in the hand. The Purple is so dark it appears black on a cloudy day. This specimen was difficult to photograph. One pic is backlit with a torch, other pics taken out doors on cloudy and bright sun days. There are some interesting internal zoning patterns also visible in the photos.
Wyloo Station, Western Australia.
5.7cm x 4.8cm x 4.1cm, 79g.
Quartz is a fascinating common mineral, found in the Earth’s crust. If pure, quartz forms colourless, transparent hard crystals with a glass like luster. A significant component of many igneous, metamorphic and sedimentary rocks. Found in an abundant variety of formations and colors.
Polished Quartz was the most advanced technology thousands of years ago, used by the Assyrians. As a lens to focus light, could help start a fire for cooking. The Vikings could have used one of these to find the sun on a cloudy day. As a magnifying glass the ancients could see the stars too. Today it leads technology being the main component of transistors which make our computers work and solar panels.
The presence of trace elements gives an abundance of color range and crystal forms. Quartz is hard 7, light 2.65 and just adorable with an amazing shine when polished. No cleavage, characteristic conchoidal fracture and strongly piezoelectric and pyroelectric. Interestingly except in Twins where the opposites cancel each other out.
Chemistry: SiO2 , Silicon dioxide
Uses: silica for glass, electrical components, optical lenses, abrasives, gemstones, ornamental stone, specimens, building stone, etc.
Variety specimens include.
Amethyst is the purple gemstone variety.
Citrine is the yellow to orange gemstone variety. It is rare in nature and often created by heating Amethyst.
Milky Quartz is the cloudy white variety.
Rock crystal is clear quartz and used as a gemstone.
Rose quartz is a pink to reddish pink variety.
Smoky quartz is the brown to gray variety.
Clear quartz is the most common color then white or cloudy milky quartz. Purple (Amethyst), pink (Rose Quartz), gray or brown to black (Smoky Quartz) are also common.
Luster is glassy to vitreous as crystals, while cryptocrystalline forms are usually waxy to dull but can be vitreous.
Transparency: Crystals are transparent to translucent, cryptocrystalline forms can be translucent or opaque.
Crystal System is trigonal; 3 2.
Crystal Habits are again widely variable. A prominent habit is hexagonal prisms, terminated with a six sided pyramid. This is two rhombohedrons. Three of the six sides of the pyramid may dominate causing the pyramid to be or look three sided. Left and right handed crystals are possible and identifiable only if minor trigonal pyramidal faces are present. Druse forms (crystal lined rock with just the pyramids showing) are also common. Massive forms can be just about any type but common forms include botryoidal, globular, stalactitic, agate.
Cleavage is very weak in three directions (rhombohedral).
Fracture is conchoidal.
Hardness is 7, less in cryptocrystalline forms.
Specific Gravity is 2.65 or less if cryptocrystalline. (average)
Streak is white.
Other Characteristics: Striations on prism faces run perpendicular to C axis, piezoelectric (see tourmaline) and index of refraction is 1.55.
Associated Minerals are numerous and varied but here are some of the more classic associations of quartz. Amazonite a variety of microcline, tourmalines especially elbaite, wolframite. But wait there’s more pyrite, rutile, zeolites, fluorite, calcite, gold, muscovite, topaz, beryl, hematite and spodumene.
Notable Occurrences of amethyst are Brazil, Uraguay, Mexico, Russia, Thunder Bay area of Canada, and some locallities in the USA. For Smoky Quartz; Brazil, Colorado, Scotland, Swiss Alps among many others. Fine examples of Rock crystal come from Brazil, Arkansas, many localities in Africa. Fine Agates come from Brazil, Lake Superior, Montana, Mexico and Germany.
Best Field Indicators are first the fact that it is very common. Then crystal habit, hardness, striations, good conchoidal fracture and lack of good cleavage. Assume transparent clear crystals may be quartz.