Red Phosphorus powder. 
Phosphorus comes in several allotropic forms.  Red phosphorus is reasonably safe, and not likely to spontaneously explode or anything.  Not so white phosphorus: That has to be kept under water, or preferably not kept at all.  It's the form that glows in the dark because of the spontaneous reaction with air on its surface.  Funny how the bonding structure can make such a difference. 
 
Click the source link for an interesting story about where this sample came from. 
Source: Tryggvi Emilsson and Timothy Brumleve 
Contributor: Tryggvi Emilsson and Timothy Brumleve 
Acquired: 6 September, 2002 
Text Updated: 16 April, 2009 
Price: Donated 
Size: 0.75" 
Purity: >99% 
Sample Group: Powders
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