The head looks like it was applied,the side view with what look like shoulder/chest appears to have a "painted" surface with bubbles.
They are even made in China and other locations and sold...
Chalcedony................. http://www.minerals.net/gemstone/chalcedony_gemstone.aspx
The photos are too blurry,but it a little like Victoria stone.
Looks like a Dendritic Agate and may be dyed.
Gemstone facet edges can be rounded and glass facet edges can be sharp,it's not a fool proof way to tell the difference.
Popular lead cast soldiers,etc. with kits available in a number of countries. https://www.ebay.com/b/Lead-Soldier-Mold/152938/bn_55190425
https://www.brilliance.com/education/diamond-size-chart
The photos are out of focus,but it looks like an open seam and some kind of a poor repair on the rim of the cup.
Optivisor,dental surgical glasses,etc.
How many hundreds of 54mm lenses have you cut and polished? Could have been used for multiple purposes.
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