![calcite and apatite [67 kb]](2226.jpg)
"Rock of the Month # 1, posted July 2001" --- Sample 2226, digital photo by Thach Bui, 2001
Apatite is a widespread mineral, a calcium phosphate, historically a source of phosphate for fertilizer. This striking sample comes from a long-abandoned apatite mine in the Lake Clear area, Sebastopol Twp., Renfrew County. The Lake Clear region of the Proterozoic Grenville province in southeastern Ontario hosts at least four apatite deposits (Grice and Gault, 1982), which produced a total of perhaps 2,000 tonnes of apatite in the 1880s. This sample, 13x11x8 cm in size, displays unusual prismatic maroon-red apatite crystals, best-developed where they can grow easily into coarse rhombohedral calcite in presumed calcite veins cutting syenitic host rocks. The rock is composed of white and orange calcite (the latter in rhombs up to 4 cm wide), red apatite and dark green amphiboles. It also contains a trace of dark sphene and rare apatite of typical green colour (found only where totally enclosed by orange calcite). This sample is probably mine "waste", as the ore was dominated by massive, granular, fine-grained red apatite. Besides calcite and apatite, a sample of the granular ore contains hornblende plus accessory actinolite, biotite, magnetite, hematite and plagioclase feldspar. The apatite of the region is enriched in Y and some REE (yttrium and rare- earth elements). The causes of the mineral colours are not known for certain. The bright orange calcite is reputed to fade in bright sunlight: no fading was noted in a test rhomb placed in a sunny place for 90 days. Orange calcite is known also from Freiberg (Germany), Montana Mountain (Yukon, Canada) and, like red apatite, from other parts of the Bancroft-Renfrew region of Ontario (see, e.g., Sabina, 1971).
References
GRICE,JD and GAULT,RA (1982) The Clear Lake-Kuehl Lake area, Renfrew County, Ontario. Mineralogical Record 13 no.4, 209-213.
SABINA,AP (1971) Rocks and Minerals for the Collector: Ottawa to North Bay,Ontario: Hull to Waltham, Quebec. GSC Pap. 70-50, 130pp.