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Can you identify this rock

What is this black mineral? Seems to have formed at same time as the quartz. Streak is light gray. With some difficulty I can scrape it with my fingernail, produces light gray powder. Has a powdery feel. A pearly shimmer. Bubble pockets. Found in central NC, about 10 miles from a pyrophllite quary.

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Nov 04, 2020
by: Douglas

You have done your homework! Good for you.

Pyrophllite is my best guess. If you go to the middle of the page below, there is a chart of minerals listed by hardness. A fingernail is about 2.5 on the mohs scale. Comparing all of the minerals at 2.5 or less is pyrophllite. Since you know there is pyrophllite in the area that would be my first choice. Most of the image samples I found are light colored but there are some that are a gray like your specimen. Look at the details of your specimen and see if they match descriptions of pyrophllite.

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