Canadian Rockhound: The UK58 Group

The UK58 Group: Quintinite-3T, Charmarite-2H, Charmarite-3T, and Caresite-3T
Abstracted by Malcolm Back

This new group of carbonate minerals have the general formula M₄²⁺Al₂³⁺
(OH)₁₂CO₃^.3H₂O (or 4:2 minerals), including charmarite-2H and charmarite-3T in which M=Mn, quintinite-2H and quintinite-3T in which M=Mg and caresite-3T in which M=Fe. All were found and described from Mont-Saint Hilaire, except for the quintinite-2H which is from the Jacupiranga mine, São Paulo, Brazil. At Mont Saint-Hilaire these species occur as late-stage hydrothermal minerals in miarolitic cavities and in pegmatite bodies within the nepheline syenite. Samples of these minerals were originally given the designation UK58 group.

Charmanite-2H
Charmarite-2H, Charles and Marcelle Weber specimen. Royal Ontario Museum. Photo by Violet Anderson. ©1998 R.O.M.

Charmarite-2H, named for Charles and Marcel Weber was collected by the Webers in 1971 and 1976 from the Demix quarry. Other specimens were collected by Jan Van Luling in 1975 from Demix, and by Stephen and Janet Cares in 1988 from the Poudrette quarry. Charmarite-3T was collected by the Cares in 1975 from the Demix quarry. Both polytypes of charmarite are associated with analcime, natrolite, microcline, aegerine, astrophyllite, tetranatrolite, catapleiite, calcite, siderite, rhodochrosite, burbankite, kutnohorite and an amorphous phase.

Charmarite-2H occurs as tabular hexagonal crystals to 0.5 mm. across, commonly stacked along [0001] to form pagoda-like aggregates up to 1 mm. Long, and as thin mica-like plates in some cases forming star-shaped aggregates. The stacked tabular crystals can show parallel-growth features along [0001]. The most common forms observed are {0001} and {10(bar1)0}. It is transparent, with a vitreous lustre, orange-brown, pale brown, pale blue or colourless, and the streak is white. There is one perfect cleavage {0001}, and an uneven fracture. The Mohs hardness is about 2, and it is non-fluorescent in ultraviolet light. The mineral is attacked by 1:1 HCl (hydrochloric acid) and HNO₃ (nitric acid) with effervescence, and dissolves in H₂SO₄ (sulfuric acid) with effervescence. Charmarite-2H is uniaxial negative, w 1.587(1) and e 1.547(1), with weak pleochroism in the pale-blue varieties, w = colourless e = pale-blue, and strong pleochroism in the orange-brown varieties, w = orange-brown e = very pale brown. It is hexagonal, space group P6₃22, a 10.985(5) c 15.10(2) Å, V 1578(3) Å and Z = 4. D_calc. = 2.50 g/cm³ and D_meas. = 2.47(1) g/cm³.

Charmanite-3T
Charmarite-3T, Charles and Marcelle Weber specimen.
Royal Ontario Museum. Photo by Violet Anderson. ©1998 R.O.M.

Charmarite-3T occurs as thin {0001} plates forming caps at the free end of prismatic crystals, or as stacked tabular crystals that taper off at the other end to give an appearance of a nail. The most common forms observed are {0001} and {10 0}. It is transparent, with a vitreous lustre, orange-brown to pale brown, and the streak is white. There is one perfect cleavage {0001}, and an uneven fracture. The Mohs hardness is about 2, and it is non-fluorescent in ultraviolet light. The mineral is attacked by 1:1 HCl and HNO₃ with effervescence, and dissolves in H₂SO₄ with effervescence. Charmarite-3T is uniaxial negative, w 1.587(1) and e undetermined, pleochroic with w = brown e = pale brown. It is trigonal, space group P3₁12 or P3₂12, a 10.985(3) c 22.63(3) Å, V 2366(4) Å and Z = 6. D_calc. = 2.50 g/cm³ and D_meas. = 2.48(1) g/cm³.

Quintinite-3T, László Horváth specimen. Royal Ontario Museum. Photo by Violet Anderson. ©1998 R.O.M.

Quintinite-3T, named for Quintin Wight, was collected from the second level of the Demix quarry in 1973 by Lázló and Elsa Horváth. It is associated with analcime, natrolite, tetranatrolite, aegerine, calcite, siderite, fluorite, pyrite, biotite, donnayite-(Y) and ancylite(Ce).

Quintinite-3T occurs as hexagonal tabular crystals on {0001} to 1 mm across, commonly forming rosettes, in some cases in an epitactic relationship with donnayite-(Y). Common forms observed are {0001} and {10(bar1)0}. It is transparent, with a vitreous lustre, bright yellow to pale yellow and the streak is white. There is one perfect cleavage {0001}, and an uneven fracture. The Mohs hardness is about 2, and it is non-fluorescent in ultraviolet light. The mineral is attacked slightly by 1:1 HCl, strongly by HNO₃, and dissolves in 1:1 H₂SO₄. Quintinite-3T is uniaxial positive or negative, w 1.533(1) and e 1.533(1), both the same within the error of measurement (0.0001), and most are non-pleochroic. One sample with Mg:Fe of ~1 is pleochroic with w = dark green, e = light green. It is trigonal, space group P3₁12 or P3₂12, a 10.558(2) c 22.71(3) Å, V 2192(3) Å and Z = 6. D_calc. = 2.14 g/cm³ and D_meas. = 2.14(1) g/cm³.

Quintinite-3T, Bob Ramik specimen. Royal Ontario Museum. Photo by Violet Anderson. ©1998 R.O.M.

Caresite-3T, named for Stephen and Janet Cares, was collected from the Poudrette quarry by the Cares in 1989 and by George Chao in the 1980's. It was also found in 1955 by Dr. Peter Tarasoff in the old Corporation quarry on Mont Royal, Montreal, and the site is now inaccessible.

Caresite-3T occurs tabular crystals on {0001} and pyramidal crystals to 0.5 mm across, forming irregular aggregates. Forms observed are {0001} and {10(bar1)0}, generally with a hexagonal pyramid which is not consistent with the symmetry. This apparent form may be caused by a combination of an {h0(bar h)1} trigonal dipyramid and an {hh(bar2)(bar h)l} rhombohedron or by a diminishing pinacoid during crystal growth. It is transparent, with a vitreous lustre, green-black, but it is normally coated with a fine-grained smectite or with chamosite. There is one perfect cleavage {0001}, and an uneven fracture. The Mohs hardness is about 2, and it is non-fluorescent in ultraviolet light. The mineral dissolves in 1:1 HCl, is strongly attacked by HNO₃ and H₂SO₄, with effervescence. Caressite-3T is uniaxial negative, w 1.599(1) and e 1.570(1). It is trigonal, space group P3₁12 or P3₂12, a 10.805(3) c 22.48(3) Å, V 2273(4) Å and Z = 6. D_calc. = 2.59 g/cm³ and D_meas. = 2.59(1) g/cm³.

Source:

Chao, G.Y. & Gault, R.A.(1997). Quintinite-2H, Quintinite-3T, Charmarite-2H, Charmarite-3T and Caresite-3T, a new group of carbonate minerals related to the Hydrotalcite - Manasseite group. Can. Min. 35:1541-1549.

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