Rafferty J.P. (ed.) Minerals

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7 Minerals 7

282

name colour lustre mohs

hardness

specific

gravity

litharge red greasy to

dull

2 9.1–9.2

magnetite black to

brownish black

metallic to

semimetal-

lic

5½–6½ 5.2

manganite dark steel gray

to iron black

submetallic 4 4.3–4.4

massicot sulfur to orpi-

ment yellow

greasy to

dull

2 9.6

periclase colourless to

grayish; also

green, yellow,

or black

vitreous 5½–6 3.6–3.7

perovskite

(often

contain-

ing rare

earths)

black; grayish

or brownish

black; reddish

brown to yellow

adamantine

to metallic

5½ 4.0–4.3

psi-

lomelane

iron black to

dark steel gray

submetallic

to dull

5–6 4.7

pyrochlore brown to black

(pyro); pale yel-

low to brown

(micro)

vitreous or

resinous

5–5½ 4.2–6.4

pyrolusite light steel gray

to iron black

metallic 2–6 4.4–5.0

rutile reddish brown

to red; variable

metallic

adamantine

6–6½ 4.2–5.5

spinel various vitreous 7½–8 3.55

tenorite steel or iron

gray to black

metallic 3½ 5.8–6.4

283

OxIDe MINerAlS

name habit f

rac-

ture or

cleavage

refractive

indices or

polished

section data

crystal

system

anatase pyramidal

or tabular

crystals

two

perfect

cleavages

omega = 2.561

epsilon = 2.488

extremely

variable

tetragonal

boehmite disseminated

or in pisolitic

aggregates

one very

good

cleavage

alpha = 1.64–1.65

beta = 1.65–1.66

gamma =

1.65–1.67

ortho-

rhombic

brookite only as crys-

tals, usually

tabular

subcon-

choidal

to uneven

fracture

alpha = 2.583

beta = 2.585

gamma =

2.700–2.741

ortho-

rhombic

brucite tabular

crystals;

platy aggre-

gates; ﬁbrous

or foliated

massive

one

perfect

cleavage

omega =

1.56–1.59

epsilon =

1.58–1.60

hexagonal

7 carbonates and other Minerals 7

name colour lustre mohs

hardness

specific

gravity

thorianite dark gray to

brownish black

and bluish

hornlike to

submetallic

6½ 9.7–9.9

uraninite steel to velvet

black; grayish,

greenish

submetallic

to greasy or

dull

5–6 6.5–8.5

(massive);

8.0–10.0

(crystals)

7 Minerals 7

284

name habit frac-

ture or

cleavage

refractive

indices or

polished

section data

crystal

system

cassiterite repeatedly

twinned

crystals;

crusts and

concretions

one

imperfect

cleavage

omega =

1.984–2.048

epsilon =

2.082–2.140

light gray;

strongly

anisotropic

tetragonal

chromite granular to

compact

massive

no cleav-

age;

uneven

fracture

n = 2.08–2.16

brownish gray-

white; isotropic

isometric

chryso-

beryl

tabular or

prismatic,

commonly

twinned,

crystals

one

distinct

cleavage

alpha = 1.746

beta = 1.748

gamma = 1.756

ortho-

rhombic

columbite prismatic

crystals,

often in

large groups;

massive

one

distinct

cleavage

brownish gray-

white; weakly

anisotropic

ortho-

rhombic

corundum pyramidal or

barrel-shaped

crystals;

large blocks;

rounded

grains

no cleav-

age;

uneven to

conchoidal

fracture

omega =

1.767–1.772

epsilon =

1.759–1.763

hexagonal

285

name habit frac-

ture or

cleavage

refractive

indices or

polished

section data

crystal

system

cuprite octahedral,

cubic, or

capillary

crystals; gran-

ular or earthy

massive

conchoidal

to uneven

fracture

n = 2.849

bluish white;

anomalously

anisotropic and

plechroic

isometric

delafossite tabular

crystals;

botryoidal

crusts

one

imperfect

cleavage

rosy brown-

white; strongly

anisotropic;

distinctly

pleochroic

hexagonal

diaspore thin, platy

crystals; scaly

massive;

disseminated

one

perfect

cleavage,

one less so

alpha =

1.682–1.706

beta =

1.705–1.725

gamma =

1.730–1.752

ortho-

rhombic

euxenite prismatic

crystals;

massive

conchoidal

to subcon-

choidal

fracture

n = 2.06–2.25 ortho-

rhombic

franklinite octahedral

crystals;

granular

massive

n = about 2.36

white; isotropic

isometric

gibbsite tabular crys-

tals; crusts

and coatings;

compact

earthy

one

perfect

cleavage

alpha = 1.56–1.58

beta = 1.56–1.58

gamma =

1.58–1.60

mono-

clinic

7 carbonates and other Minerals 7

7 Minerals 7

286

name habit frac-

ture or

cleavage

refractive

indices or

polished

section data

crystal

system

goethite prismatic

crystals;

massive

one

perfect

cleavage,

one less so

alpha =

2.260–2.275

beta =

2.393–2.409

gamma =

2.398–2.515

gray; strongly

anisotropic

ortho-

rhombic

hausman-

nite

pseudo-

octahedral

crystals;

granular

massive

one nearly

perfect

cleavage

omega =

2.43–2.48

epsilon =

2.13–2.17

gray-white;

distinctly

anisotropic

tetragonal

hematite tabular crys-

tals; rosettes;

columnar or

ﬁbrous mas-

sive; earthy

massive;

reniform

masses

cleavage

omega =

2.90–3.22

epsilon =

2.69–2.94

anisotropic;

weakly pleo-

chroic; often

shows lamellar

twinning

hexagonal

ilmenite thick, tabular

crystals;

compact

massive;

grains

no cleav-

age;

conchoidal

fracture

n = about 2.7

grayish white;

anisotropic

hexagonal

287

name habit frac-

ture or

cleavage

refractive

indices or

polished

section data

crystal

system

lepido-

crocite

ﬂattened

scales;

isolated

rounded

crystals;

massive

one

perfect

cleavage,

one less so

alpha = 1.94

beta = 2.20

gamma = 2.51

gray-white;

strongly aniso-

tropic and

pleochroic

ortho-

rhombic

litharge crusts; altera-

tion product

on massicot

one

cleavage

omega = 2.665

epsilon = 2.535

tetragonal

magnetite octahedral

crystals;

granular

massive

n = 2.42

brownish gray;

isotropic

isometric

manganite prismatic

crystals,

often in bun-

dles; ﬁbrous

massive

one very

perfect

cleavage,

two less so

alpha = 2.25

beta = 2.25

gamma = 2.53

brownish gray-

white; aniso-

tropic; weakly

pleochroic

mono-

clinic

massicot earthy or

scaly massive

two

cleavages

alpha = 2.51

beta = 2.61

gamma = 2.71

ortho-

rhombic

periclase irregular,

rounded

grains;

octahedral

crystals

one

perfect

cleavage

n = 1.730–1.746 isometric

7 carbonates and other Minerals 7

7 Minerals 7

288

name habit frac-

ture or

cleavage

refractive

indices or

polished

section data

crystal

system

perovskite

(often

contain-

ing rare

earths)

cubic

crystals

uneven to

subcon-

choidal

fracture

n = 2.30–2.38

dark bluish gray

ortho-

rhombic

psi-

lomelane

massive;

crusts;

stalactites;

earthy

masses

ortho-

rhombic

pyro-

chlore

octahedral

crystals;

irregular

masses

subcon-

choidal

to uneven

fracture

n = 1.93–2.02 isometric

pyrolusite columnar

or ﬁbrous

massive;

coatings and

concretions

one

perfect

cleavage

cream-white;

distinctly

anisotropic;

very weakly

pleochroic

tetragonal

rutile slender to

capillary

prismatic

crystals; gran-

ular massive;

as inclu-

sions, often

oriented

one

distinct

cleavage

omega =

2.556–2.651

epsilon =

2.829–2.895

tetragonal

289

CHROMATE MiNERAlS

Chromate minerals make up a small group of rare inorganic com-

pounds that have formed from the oxidation of copper-iron-lead

sulﬁde ores containing minor amounts of chromium. A noteworthy

occurrence is at Dundas, Tasm., known for its large, brilliant orange

prismatic crystals of crocoite; of trivial economic importance,

7 carbonates and other Minerals 7

name habit frac-

ture or

cleavage

refractive

indices or

polished

section data

crystal

system

spinel octahedral

crystals;

round or

embed-

ded grains;

granular to

compact

massive

n = 1.715–1.725 isometric

tenorite thin aggre-

gates or

laths; curved

plates or

scales; earthy

masses

conchoidal

fracture

light gray-

white; strongly

anisotropic;

pleochroic

mono-

clinic

thorianite rounded

cubic

crystals

uneven to

subcon-

choidal

fracture

n = about 2.2

(variable)

isotropic

isometric

uraninite crystals;

massive;

dendritic

aggregates of

crystals

uneven to

conchoidal

fracture

light brownish

gray; isotropic

isometric

7 Minerals 7

290

Phosphate Minerals

Phosphate minerals constitute a group of naturally occur-

ring inorganic salts of phosphoric acid, H

(PO

). More

than 200 species of phosphate minerals are recognized,

and structurally they all have isolated (PO

) tetrahedral

units. Phosphates can be grouped as: (1) primary phos-

phates that have crystallized from a liquid; (2) secondary

phosphates formed by the alteration of primary phos-

phates; and (3) ﬁne-grained rock phosphates formed at low

temperatures from phosphorus-bearing organic material,

primarily underwater.

Primary phosphates usually crystallize from aque-

ous ﬂuids derived from the late stages of crystallization.

Particularly common in granitic pegmatites are the

primary phosphates apatite [Ca

(F,Cl,OH)(PO

)

triphylite [LiFePO

], lithiophilite [LiMnPO

], and the

rare-earth phosphates monazite [(LaCe)(PO

)] and xeno-

time [Y(PO

)]. Primary phosphates commonly occur in

ultramaﬁc rocks (i.e., those very low in silica), including

carbonatites and nepheline syenites. Metamorphic apa-

tite occurs in calc-silicate rocks and impure limestones.

Secondary phosphates are extremely varied, forming

at low temperatures, in the presence of water, and under

crocoite is one of the most highly prized of minerals among collec-

tors and museums.

The basic structural unit of the chromate minerals is a tetra-

hedron formed from four oxygen atoms, each at one corner of a

tetrahedron surrounding a central chromium atom; thus each CrO

tetrahedron has a net electric charge of -2, which is neutralized by

metal ions outside the tetrahedron.

291

phOSphATe MINerAlS

name colour lustre M

ohs’

hard-

ness

specific

gravity

amblygo-

nite

white to creamy

white; slightly

tinted

vitreous to

greasy

5½–6 3.0–3.1

apatite

carbonate-

apatite

variable, greens

predominating

vitreous 5 2.9–3.2

chlorapatite

ﬂuorapatite

hydroxyl-

apatite

autunite lemon yellow to

sulfur yellow;

greenish yellow

to pale green

vitreous to

pearly

2–2½ 3.1–3.2

brushite colourless to pale

yellow

vitreous or

pearly

2½ 2.3

collophane

(massive

apatite)

grayish white;

yellowish; brown

weakly vitre-

ous to dull

3–4 2.5–2.9

lazulite azure blue or

sky blue; bluish

white, bluish

green; deep blue

vitreous 5½–6 3.1–3.4

7 carbonates and other Minerals 7

variable oxidation states. Both di- and tri-valent oxidation

states of iron and manganese are usually present, produc-

ing brilliant colours. Two common species are strengite

[Fe(PO

)(H

] and vivianite [Fe

(PO

)