My rock and mineral collection grows thanks to Antique Trove, Denio’s flea market, and kind donations of family, the rocks originating, sadly, from an inheritance: RIP Ollie. I’ll start here with quartz crystals, also called rock crystals, and post about my other new rocks in future.
Quartz, made of silicon dioxide (SiO2), aka silica, is the most abundant and widely distributed mineral found on Earth’s surface so it’s appropriate I have more crystals of quartz than any other mineral or rock in my new collection.
Quartz is the last mineral to form in a felsic (granitic) rock, and can generally be found filling in between all of the other minerals.
It occurs all over the world and forms in all temperatures so quarries are plentiful but the sea floors and rocks even deeper have little quartz, being formed mostly of mafic basalt and heavier rocks with more iron and magnesium and less silicon and aluminum.
Quartz forms in all rock types and its durable resistance to both chemical and mechanical weathering make it ubiquitous on mountaintops; and quartz makes sand for beaches of the desert and river.
This post features the quartz called rock crystal, the purest quartz, well made crystals of which consist of six-sided prisms with a six-sided pyramid at, ideally, both ends, often showing horizontal striations (like my fingernails).
To stand up to the rough and tumble of daily use as jewelery a gemstone should be at least the hardness of quartz, which is the very mineral that defines hardness rating 7 on the Mohs scale.
Here’s the normal 6-sided termination but quartz also terminates in weird ‘artichoke’ and ‘scepter’ growth forms, among other strange patterns.
Next rock post we’ll stay with SiO2 but introduce some color.
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