Pink Rock I always find quartzite to be a fascinating rock because of that pale red color. Imagine y

Pink RockI always find quartzite to be a fascinating rock because of that pale red color. Imagine your average pile of beach or desert sand – if it’s pure enough, it might well be a quartzarenite, a rock made of over 90% quartz sand grains. Quartz is a stable during metamorphism; it may change its grain size as it gets strained and bent, but if you start off with a pile of quartz and metamorphose it, you wind up with, well, a pile of quartz. A pile of metamorphic quartz is called a quartzite – this is an example of one from the Harpers Formation in the Blue Ridge Mountains of Virginia.This rock started off as sediments deposited after the breakup of the supercontinent Rodinia, when the east coast of Laurentia (the continent today at the core of North America) became a passive margin and sediments from the continent piled up along its slope. Eventually, those sediments were caught in-between Gondwanaland and Laurentia when the ocean between them closed, and during the mountain building they were metamorphosed into the units found today.The pale red or pink color is surprisingly common, I find, in quartzites. Quartz itself is colorless – it needs to have an impurity of some element or radiation damage to give it a color. However, quartz-rich rocks like this often have a reddish color to them. A rock that was truly 100% pure quartz would be basically colorless, however this rock is probably only 98% quartz or something close to that. Because quartz itself is nearly transparent, if there is anything in the rock that has a strong color, such as a bit of hematite in-between the quartz grains, the rock comes out looking red. This rock is basically stained red by the tiniest bit of hematite in-between the grains, and in fact you can see a few “measles” at the bottom where there’s a bit more hematite in single spots.-JBBImage credit: James St. Johnhttps://flic.kr/p/24uDSe7 -- source link

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