Spruce Pine Mining District, North Carolina, USA. Reference: Clifford Frondel,1958,Systematic Mineralogy of Uranium and Thorium,USGS Bulletin 1064,pg.86. ⓘ Vermiculite. Formula: Mg 0.7 (Mg,Fe,Al) 6 (Si,Al) 8 O 20 (OH) 4 · 8H 2 O. Localities: Reported from at least 24 localities in this region.