Aragonite (aka Flos-Ferri) - Santa Eulalia, Mexico (MS-2751a)
Aragonite chemically identical to Calcite. And, going back as far as Roman times was known for its beauty and hardness...leading to the name Flos-Ferri (Flowers of Iron). Measures about 11cm x 9cm x 7cm.
Will require a USPS Medium Priority Mail Flat Rate box. But, likely leaves room for additional items in the box.