U.S. Borax Mine, Kramer Borate deposit, Boron, Kramer District, Kern Co., California, USA
A lustrous, blocky crystal of yellow Calcite, with pronounced striations and tiny acicular features on its surface, has grown atop, engulfed and is replacing fibrous white Ulexite. This is an excellent and rare example of partial replacement of Ulexite by Calcite from Boron.
ex. Marty Houhoulis (Denver) collection