(Mg; Fe2+ )5 (SiO4 )2 (F; OH)2

Chondrodite

c 2001 Mineral Data Publishing, version 1.2°

Crystal Data: Monoclinic. Point Group: 2=m: Crystals rare, varied in habit, typically°attened k [010], to 10 cm. Commonly as rounded grains, massive. Twinning: On f001g,common, simple and lamellar; possibly k f015g and f305g.
Physical Properties:
Cleavage: f100g indistinct; parting on f001g. Tenacity: Brittle.
Hardness = 6{6.5 D(meas.) = 3.16{3.26 D(calc.) = 3.177
Optical Properties: Transparent to translucent. Color: Light yellow, yellow, brown, red; inthin section, pale yellow or brown to colorless. Luster: Vitreous to resinous.
Optical Class: Biaxial (+). Pleochroism: X = colorless, very pale yellow, brownish yellow;
Y = colorless, yellow-green; Z = colorless, pale green. Orientation: Z = b; X ^ c = 22± {31± .
Dispersion: r > v; strong to weak. ® = 1.592{1.643 ¯ = 1.602{1.655 ° = 1.621{1.676
2V(meas.) = 71± {85±Cell Data: Space Group: P 21 =c: a = 7.8404(2)¯ = 109± 20 Z = 2b = 4.7284(3)c = 10.2539(3)X-ray Powder Pattern: Tilly Foster mine, New York, USA. (ICDD 12-527).
2.258 (100), 1.740 (70), 3.02 (45), 2.510 (45), 3.56 (35), 2.758 (35), 2.288 (35)Chemistry:
SiO2
TiO2
Al2 O3Fe2 O3
FeO
MnO

(1)
33.60
0.06
0.24
0.05
0.86
0.16

(2)
32.16
0.20
0.73
0.60
6.08
1.35

MgO
CaO
F
H2 O+
H2 O¡
¡O = F2Total

(1)
59.30
0.00
6.61
1.46
0.00
2.78

(2)
53.21
0.00
7.11
1.20
0.00
2.99

99.56

99.65

(1) Hangelby, Finland; corresponds to (Mg5:13 Fe2+
0:04 Al0:02 Mn0:01 )§=5:20 Si1:95 O8[F1:21 (OH)0:56 O0:23 ]§=2:00 : (2) Kafveltorp, Sweden; corresponds to (Mg4:74 Fe2+
0:30 Mn0:07
Al0:05 Fe3+
0:03 Ti0:01 )§=5:20 Si1:92 O8 [F1:34 (OH)0:48 O0:18 ]§=2:00 :Polymorphism & Series:
Mineral Group:Forms a series with alleghanyite.

Humite group.

Occurrence: In contact metamorphic zones, in limestones and dolostones, associated with felsic
to alkalic plutonic rocks, especially with Fe-B-F metasomatism; in a carbonatite.
Association: Phlogopite, spinel, magnetite, grossular, wollastonite, forsterite, monticellite,cuspidine, diopside, calcite.
Distribution: From Pargas, Hangelby, and Sibbo, Finland. At Kafveltorp, near Kopparberg,
Sweden. From Monte Somma and Vesuvius, Campania, Italy. At Le Chipal, Vosges, France. From
Bhandara, Maharashtra, India. In the USA, ¯ne crystals from the Tilly Foster mine, Brewster,
Putnam Co., and Amity, Orange Co., New York; at Franklin and Sparta, Sussex Co., NewJersey; Johnson Camp, Cochise Co., and the Lakeshore mine, Pinal Co., Arizona; and Crestmore,Riverside Co., California. From Bancroft, Ontario, Canada. In the Loolekop carbonatite,Transvaal, South Africa. A few other localities are known.
Name:

From the Greek meaning grain, alluding to its occurrence in isolated grains.

References: (1) Dana, E.S. (1892) Dana's system of mineralogy, (6th edition), 536{538.
(2) Deer, W.A., R.A. Howie, and J. Zussman (1982) Rock-forming minerals, (2nd edition),v. 1A, orthosilicates, 379{417. (3) Gibbs, G.V., P.H. Ribbe, and C.P. Anderson (1970) Thecrystal structures of the humite minerals. II. Chondrodite. Amer. Mineral., 55, 1182{1194.
(4) Phillips, W.R. and D.T. Gri®en (1981) Optical mineralogy, 142{144.
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