Cleavage Perfect Fracture Uneven Mohs Scale hardness 1.5-2 Luster Vitreous Streak Pale yellow Specific gravity 2.4-2.7 Refractive index Translucent Pleochroism None Vermiculite is a natural mineral that expands with the application of heat . The expansion process is called exfoliation and it is routinely accomplished in purpose-designed commercial furnaces. Vermiculite is