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I got this rock a year ago at a mineral and fossil event, and there was a stand where they where selling 'mystery packages', boxes full of different fossils and minerals. I bought one, and figured out all objects but this one. Any idea what it is?

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Your specimen is smoky quartz (black) and orthoclase or microcline feldspar. The combination of smoky quartz and feldspar is a common granitic mineral assemblage seen around the world.

Your specimen looks very similar to quartz and microcline specimens from the Rocky Mountains in Colorado.

Two specimens from my personal collection from central Colorado. enter image description here enter image description here

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I believe the large white crystals are perthite - orthoclase (potassium feldspar) that has exolved to form intergrowths of sodium-rich albite feldspar.

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