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3D3DRock of alum.
This is a hunk of potassium alum, used for many things but sold retail in this form primarily as a deodorant.
Source: eBay seller saratthasamuccaya
Contributor: Theodore Gray
Acquired: 8 February, 2009
Text Updated: 8 February, 2009
Price: $6/pound
Size: 3"
Composition: KAl(SO4)2.12H2O