K1−1.5 (Mn4+ , Mn3+)8 O16

Cryptomelane

c 2001-2005 Mineral Data Publishing, version 1

Crystal Data: Monoclinic. Point Group: 2/m. Rarely in subhedral crystals, to 2 mm;
commonly as compact fine-grained masses, banded colloform, botryoidal, or radial fibrousaggregates, all in the same specimen; massive cleavable. Twinning: Typically on (010) and (101),producing a pseudotetragonal unit cell.
Physical Properties: Fracture: Conchoidal. Tenacity: Brittle. Hardness = 6–6.5, compact.
D(meas.) = 4.17–4.41 D(calc.) = [4.44]
Optical Properties: Opaque. Color: Steel-gray to bluish gray when fresh; tarnishes to dullgrayish black; light tan or gray in reflected light. Streak: Brownish black. Luster: Metallic todull.
Optical Class: Isotropic, nearly.
R: n.d.
Cell Data:
Z = [1]

Space Group: I2/m. a = 9.956(3)b = 2.8705(9)c = 9.706(4)β = 90.95(3)◦X-ray Powder Pattern: Philipsburg, Montana, USA.
2.39 (10), 6.90 (9), 4.90 (8), 3.10 (8), 2.15 (6), 1.83 (6), 1.54 (6)Chemistry:
SiO2
TiO2
MnO2
Al2 O3Fe2 O3MnO
CoO
NiO
CuO
ZnO

(1)
0.58
0.01
83.13
0.37
0.46
2.08
0.00
0.00
0.12
5.23

Mineral Group:

Cryptomelane group.

(2)
0.18
0.00
87.09
0.39
0.19
2.49
0.08
0.00
0.00
1.69

(3)

84.41
0.99
3.03

MgO
CaO
SrO
BaO
Na2 O
K2 O
H2 O+
H2 O−
P2 O5

(1)
0.05
0.27
0.00
0.13
0.44
3.50
2.58
0.81
0.07

(2)
0.07
0.00
0.00
0.00
0.48
3.10
3.58
0.60
0.00

(3)
0.15
1.75
1.97
1.02
5.78

Total
99.83
99.94
[99.10](1) Tombstone, Arizona, USA; Mn4+ from “available O”. (2) Philipsburg, Montana, USA; Mn4+
from “available O”. (3) Chindwara, India; by electron microprobe, Mn4+ :Mn3+ from chargebalance, original total given as 99.18%; corresponding to (K0.94 Na0.25 Sr0.13 Ba0.10 Mg0.03 )Σ=1.45
3+
3+(Mn4+6.33 Mn1.20 Fe0.30 Al0.15 )Σ=7.98 (O, OH)16 .

Occurrence: Widespread in oxidized manganese deposits as open-space fillings or replacing
primary manganese-bearing minerals; commonly replaced by other secondary manganese minerals.
Association:Pyrolusite, nsutite, braunite, chalcophanite, manganite, other manganese oxides.

Distribution: Some localities for well-studied and pure material include: in the USA, fromthe Oregon-Prompter mine, Tombstone, Cochise Co., in the Hardshell and Mowry mines, Santa
Cruz Co., and the Artillery Mountains, Mohave Co., Arizona; at Lake Valley, Sierra Co., New
Mexico; from the Silver Cliff district, Custer Co., Colorado; at Philipsburg, Granite Co., Montana.
From Urucum, Mato Grosso, Brazil. In Oriente Province, Cuba. From Nsuta, Ghana. At Sitapar,Chindwara district, Central Provinces, India. On Groote Eylandt, Northern Territory, Australia.
Name: From the Greek for hidden and black, alluding to the mineral’s obscure identity as oneof several black mineral species in “psilomelane”, the collective term for hard manganese oxides.
Type Material:n.d.

References: (1) Richmond, W.E. and M. Fleischer (1942) Cryptomelane, a new name for thecommonest of the “psilomelane” minerals. Amer. Mineral., 27, 607–610. (2) Larson, L.T. (1964)
Geology and mineralogy of certain manganese oxide deposits. Econ. Geol., 59, 54–78. (3) Post,J.E., R.B. Von Dreele, and P.R. Buseck (1982) Symmetry and cation displacements in hollandites:
structure refinements of hollandite, cryptomelane, and priderite. Acta Cryst., 38, 1056–1065.
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