Calcite crystals

from the Grenville province of southeastern Ontario, Canada

calcite, 213 kb]

Above: coarse rosy-pink to red calcite crystals displaying typical rhombohedral crystal form and cleavage planes parallel to the crystal faces. Sample 2147 from the Childs iron mine [1] in Mayo township, northern Hastings county. The pink calcite fills a vein 5-10 cm thick, cutting granular magnetite iron ore. Calcite is soft, reacts rapidly with dilute acid, is non-magnetic, and commonly displays the crystal faces and cleavage seen above. However, it varies greatly in form and colour.

"Rock of the Month #122, posted for August 2011" ---

Calcite is one of the most common and familar minerals. Calcite varies greatly in habit (Turley and Koval, 1987; Fisher and Glenn, 1989; Brock, 1993; Richards and Robinson, 2000; Huizing et al., 2003). Goldschmidt (1913, plates 3 to 155) provided a massive review of crystal habit in calcite, from the simplest to the most baroque. The crystal system of calcite, dolomite and the other common carbonates is hexagonal (rhombohedral). Calcite cleaves readily under pressure, and in section thin twin lamellae are most often parallel to the long diagonal of the rhomb. Dolomite can appear very similar to calcite, but tends to show a pearly lustre, slower acid reaction, and often curved crystal faces, and in thin section the twin lamellae are parallel to both short and long diagonals of the rhomb.

In shallow, boiling epithermal veins and geothermal systems, calcite may form with a platy habit, that can be pseudomorphed by silica (Simmons and Christenson, 1990; Saunders, 1994; Renaut et al., 1999). In the rare case of carbonate (as opposed to silicate) magmas, dendritic growth of calcite is possible in rapid cooling (Gittins et al., 1975).

Given the outward complexity of calcite, it is no surprise that the internal growth of the mineral is just as complex, and is controlled to a degree by the presence of minor elements in the crystal lattice (e.g., Davis et al., 2000; Temmam et al., 2000).

Calcite assumes various colours, and may harbour inclusions of sulphides, native copper and many other minerals (e.g., Turley and Koval, 1987; Brock, 1993; Garvin and Tribbey, 2005). Some of the twinned forms are very complex, as in calcite from basalt cavities in Madagascar (Praszkier, 2010). Crystals range from microscopic to some tens of tonnes in size (Landis, 1983).

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Above left: a sample of pale brownish rhombohedral calcite with coarse, pale green apatite and flakes of brown phlogopite mica from the Jabez Stoness mica mine [2], Bedford township, Frontenac county. The cleavage planes of the carbonate define domains of the crystals on the fresh-broken surface: they are also visible as depressions on weathered surfaces. Indeed, textural and mineralogical features in many rocks are often easier to see when time (microbial action, freeze-thaw, acid rain, etc) has had its way with the outcrop.

Above right: a vuggy cavity lined with coarse calcite rhombs, in marble from the Actinolite area, in southern Elzevir township, Hastings county. LeeAnn Beer collection. A binocular-microscope examination of 18 calcite crystals, 1-3 cm in maximum dimension, from this site reveals ubiquitous rhombohedral cleavage traces, and less-common twinning on the long axis of the rhomb. All these planes may be slightly weathered, and darkened by unidentified material (mineral dust, and/or oxides). A further example of calcite can be seen here, a large crystal from Zacatecas
state, Mexico.

[1] The Childs iron mine (AMIS site 3325) is one of numerous iron deposits in the region (Lindeman, 1913). Many of these are magnetite iron skarns, developed along the contacts between marbles and intrusions (generally diorite). The magnetite iron deposits in northern Hastings county include the Childs, Rankin and Bessemer mines in Mayo township and the Coe Hill mine in Wollaston township (Thomson, 1943; Rose, 1958). Calcite is a common gangue mineral.
[2] The Jabez Stoness mica mine in Bedford township (AMIS site 0534) was named for one of the principals, one Jabez M. Stoness of Stoness Corners (Anon, 1900; Sabina, 1968).

References, in chronological order:

Anon (1900) Minerals of Ontario. ODM Ann.Rep. 9, for 1899, p.133.

Goldschmidt,V (1913) Atlas der Krystallformen von Victor Goldschmidt. Volume II, Calaverit- Cyanochroit. 200pp. plus 251 plates (in Ger.), reproduced by the Rochester Mineralogical Symposium, 1986.

Lindeman,E (1913) Magnetite occurrences along the Central Ontario Railway. Canada Department of Mines Report 184, 23pp., 9 plates and 1 map.

Thomson,JE (1943) Mineral occurrences in the North Hastings area. ODM Ann.Rep. 52 part 3, 80pp.

Rose,ER (1958) Iron deposits of eastern Ontario and adjacent Quebec. GSC Bull. 45, 120pp. plus 5 maps.

Sabina,AP (1968) Rocks and Minerals for the Collector: Kingston, Ontario to Lac St-Jean, Quebec. GSC Paper 67-51, 147pp.

Gittins,J, Hewins,RH and Laurin,AF (1975) Kimberlitic-carbonatitic dikes of the Saguenay River valley, Quebec, Canada. In `Physics and Chemistry of the Earth 9' (Ahrens,LH, Dawson,JB, Duncan,AR and Erlank,AJ editors), Pergamon, 940pp., 137-148.

Landis,GP (1983) Harding Iceland Spar: a new δ18O- δ13C carbonate standard for hydrothermal minerals. Isotope Geoscience 1, 91-94.

Turley,C and Koval,M (1987) The Miller calcite collection. Mineral.Record 18 no.6, 405-411.

Fisher,RW and Glenn,GH (1989) Micro Minerals of Mont Saint-Hilaire, Quebec. Published privately by the authors: R.W. Fisher, 17 Gavin Drive, St. Catharines, Ontario L2M 2X8 and G.H. Glenn, 8459 Parkway Drive, Niagara Falls, Ontario L2G 6W8. Reprinted January 1993, 166pp., sponsored by the Canadian Micro Mineral Association.

Simmons,SF and Christenson,BW (1990) Platy calcite as an indicator of boiling in epithermal deposits: evidence from New Zealand geothermal systems. GSA Abs.w.Progs. 22 no.7, 42, Dallas.

Brock,KJ (1993) The crystal forms of calcite. Mineral.Record 24, 451-461,470.

Saunders,JA (1994) Silica and gold textures in bonanza ores of the Sleeper deposit, Humboldt County, Nevada: evidence for colloids and implications for epithermal ore-forming processes. Econ.Geol. 89, 628-638.

Renaut,RW, Jones,B and Le Turdu,C (1999) Calcite lilypads and ledges at Lorusio Hot Springs, Kenya Rift Valley: travertine precipitation at the air-water interface. Can.J.Earth Sci. 36, 649-666.

Davis,KJ, Dove,PM and De Yoreo,JJ (2000) The role of Mg2+ as an impurity in calcite growth. Science 290, 1134-1137.

Richards,RP and Robinson,GW (2000) Mineralogy of the calcite-fluorite veins near Long Lake, New York. Mineral.Record 31, 413-422.

Temmam,M, Paquette,J and Vali,H (2000) Mn and Zn incorporation into calcite as a function of chloride aqueous concentration. Geochim.Cosmochim.Acta 64, 2417-2430.

Huizing,T, Jarnot,M, Neumeier,G, Richards,RP and Schneider,G (editors) (2003) Calcite: the Mineral with the Most Forms. ExtraLapis English 4, Lapis International, 114pp.

Garvin,PL and Tribbey,G (2005) The minerals of west-central Illinois. Mineral.Record 36, 421-431.

Praszkier,T (2010) Calcite and zeolites from Sambava, Madagascar. Mineral.Record 41, 239-252.

Graham Wilson, 10-13 July 2011

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