This came from a region in Chihuahua, Mexico, that no longer produces new material.
The black hemispheres of crystals around the edges of the agate are siderite, which is FeCO3, and when there is manganese in place of some of the Iron atoms it is blackish.
Approx 5" diameter and 2" thick. Total weight 4.75# +/-.
Polished to collector standard.
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