Whewellite

CaC2O4∙H2O

Crystal Data: Monoclinic. Point Group: 2/m. Equant to short prismatic [001] crystals, typicallydistorted, with {001}, {011}, {010}, {110}, {120}, {132}, {101}, several others, to 23 cm; massive
cleavable. Twinning: Common, {101} as twin and contact plane, with or without re-entrants.
Physical Properties: Cleavage: Good on {101}, imperfect on {010}, indistinct on {001}, {110}.
Fracture: Conchoidal. Tenacity: Brittle. Hardness = 2.5-3 D(meas.) = 2.21-2.23 D(calc.) = 2.258
Optical Properties: Transparent. Color: Colorless, white, may be pale yellow or pale brown;colorless in transmitted light. Luster: Vitreous, pearly on {010} and some cleavages.
Optical Class: Biaxial (+). Orientation: X = b; Z ∧ c = 30°. Dispersion: r < v. α = 1.489-1.491
β = 1.553-1.554 γ = 1.649-1.650 2V(meas.) = 80°-84°
Cell Data: Space Group: P21/c. a = 6.250(1) b = 14.471(2) c = 10.114(2) β = 109.978(5)° Z = 8
X-ray Powder Pattern: Near Havre, Montana, USA.
5.95 (100), 3.652 (90), 2.357 (80), 2.971 (50), 2.497 (20), 2.262 (20), 2.906 (10)Chemistry:

P2O5
C2O3CaO

(1)
0.01
48.68
38.27

(2)
49.29
38.38

(1)
(2)
H2O+ 13.01
H2O0.13
H2O
12.33
Total 100.10 100.00(1) Huron River, Erie Co., Ohio; here converted to oxides.

(2) CaC2O4∙H2O.

Occurrence: Of uncommon occurrence as a low-temperature primary hydrothermal mineral incarbonate-sulfide veins, geodes, or septarian nodules; may be associated with coal measures orformed by oxidation of organic material in surrounding rocks; in some uranium deposits.
Association: Calcite, barite, sphalerite, pyrite, weddellite, waxy hydrocarbons.
Distribution: Originally described from an unknown locality. Well characterized material from: inGermany, in Saxony, at Freital-Burgk, near Dresden, as large crystals; in the Himmelsfürst mine,
Erbisdorf, near Freiberg; Zwickau, and Schlema-Hartenstein; at Paitzdorf, near Ronneburg,Thuringia. From Kladno, Pchery, near Slaný (Schlan), Czech Republic. At Cigelka, Slovakia. Fromthe Boldut mine, Cavnic (Kapnikbánya), Romania, large crystals. In France, in the Saint-Sylvestre
mine, Bas-Rhin, and at Condorcet, Drôme. In the Mealbank quarry, Ingleton, North Yorkshire,England. In Russia, from the Maikop district, Caucasus Mountains, and as large crystals fromDal’negorsk, Primorskiy Kray. In the USA, from about 11 km southeast of Havre, Hill Co., Montana;near Elm Springs, Meade Co., South Dakota, very large crystals; near Biggs, Sherman Co., Oregon;
in the Radon mine, near Moab, San Juan Co., Utah; along the Huron River, about 2 km west ofMilan, Erie Co., Ohio. There are numerous other minor localities.
Name: Honors William H. Whewell (1794-1866), English naturalist and philosopher.
Type Material: [Harvard University, Cambridge, Massachusetts, USA, 78102.]
References: (1) Palache, C., H. Berman, and C. Frondel (1951) Dana’s system of mineralogy, (7thedition), v. II, 1099-1101. (2) Leavens, P.B. (1968) New data on whewellite. Amer. Mineral., 53,455-463. (3) Deganello, S. and O.E. Piro (1981) The crystal structure of calcium oxalatemonohydrate (whewellite). Neues Jahrb. Mineral., Monatsh., 81-88. (4) Pecora, W.T. and J.H. Kerr(1954) Whewellite from a septarian limestone concretion in marine shale near Havre, Montana.
Amer. Mineral., 39, 208-214. (5) Echigo, T., M. Kimata, A. Kyono, M. Shimizu, and T. Hatta(2005) Re-investigation of the crystal structure of whewellite [Ca(C2O4)] and the dehydration
mechanism of caoxite [Ca(C2O4)·3H2O]. Mineral. Mag., 69, 77-88. (6) (2005) Amer. Mineral.,90(8), 1469 (abs. ref. 5).

Mineralogical Society of America

Handbook of Mineralogy

Revised 1/6/2021