Calcite, Pyrite, Broken Hill, New South Wales

Mineral Matters #383

Calcite and pyrite are two very common minerals, but true to form, Broken Hill has some surprises.

This specimen is 40x27x25mm and a small amount of matrix is covered by colourless calcite crystals to about 5mm in length. The whole specimen glows pink under ultraviolet light, due to a layer of manganese-bearing calcite sitting between the matrix and the colourless crystals.

Then on the termination of every calcite crystal is a cluster of pyrite crystals. A few other pyrites are dotted around too.

I don’t know why this occurs. I assumed this was some sort of epitaxial growth but when you look at the definition, not so sure. If you think you know, let me know in the comments.

Ex Margaret Brown Collection. Photo shows one of the calcite crystals with the pyrite group on the termination (width of view 3.5mm).

Click on the image below for a higher resolution version.