It's a Chessex eight-sided die, part of CHX 25307 "Cobalt 7 Speckled Polyhedral Die Set", rolled on a Chessex battle map.
<a href="//commons.wikimedia.org/wiki/User:Prosfilaes" title="User:Prosfilaes">Prosfilaes</a>
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<span class="int-own-work" lang="en">Own work</span>