Assertion: mineral's crystal | /r/AtLocation | precambrian pegmatite rocks
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Source sentences:
text: Large crystals and crystal fragments of feldspar minerals occur in the Precambrian pegmatite rocks that crop out in the Llano Uplift area of Central Texas — including Blanco, Burnet, Gillespie, Llano, and Mason counties — and in the Van Horn area of Culberson and Hudspeth counties in West Texas.