This is an exceptional crystal of fluorapatite for Cerro de Mercado – the crystals are typically 1-3 cm in length, and this one is 5.3 cm, very large for the locality. The crystal is sharp, with bright, glassy faces all around. It has great yellow-green colour, and some impressive transparency for a crystal of this size. Internal crazing causes small rainbow flashes in places within the crystal. Some internal colouration from iron on the backside as you can see in the last photo. In excellent condition, very minor edge wear and a couple of tiny nicks in spots, but irrelevant to the piece – it is super. In addition to all of this, there is a great parallel-growth crystal adding real character. This is a top calibre Cerro de Mercado fluourapatite.

About These Fluorapatites

Crystals of yellow-green fluorapatite from Cerro de Mercado have been known for a long time, and at times they have been produced in abundance. However, truly fine specimens are actually hard to find, as most of the fluorapatites from the mine are badly damaged. In part this is because they have typically been collected in the past without due care (tossed into buckets and so on). But in part it is also due to their own formation history – although their geological origin is still a matter of uncertainty, the crystals always have one termination and one incomplete end (doubly-terminated crystals are not known from Cerro de Mercado) and they are cemented into the matrix, all suggestive of post-crystallization activity within the deposit. This cementing involves varying mineral constituents (some of which are rather unhelpful when it comes to extracting fine mineral specimens). In particular, excellent matrix specimens are very uncommon.

Cerro de Mercado is still a producing iron mine, and the fluorapatite crystals in this lot were collected this year. As contemporary mining and sorting/separation have become mechanized, and also owing to the fact that the apatite at the mine is now concentrated for its phosphate value, the preservation of fine fluorapatite crystals and matrix specimens is a greater challenge than it used to be. Damage is still a rampant problem. I selected the few fine pieces here out of a lot of hundreds of specimens, offered by a seller who lives beside the mine. Although it is likely that specimens will continue to be produced for as long as the mine continues to operate, it is also likely that fine undamaged specimens will continue to be hard to obtain.

The definitive article on this locality is Wendell Wilson’s excellent piece in the Mineralogical Record, Special Issue – Mexico VI, Vol. 42:5, Sept-Oct 2011.