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Minerals and Gems Help (page 2)

By — McGraw-Hill Professional
Updated on Sep 1, 2011

Mineral Groups And Properties

All minerals belong to a specific chemical group, which represents their affiliation with certain elements or compounds. The chemical structure of minerals is exact, or can vary slightly within limits. They have specific crystalline structures and belong to different groups according to the way the mineral’s atoms are arranged. Elements like gold , silver , and copper are found naturally and considered minerals.

A mineral is a naturally found, inorganic substance with a specific crystalline structure.

Minerals are classified into the following chemical groups: elements, sulfides, oxides, halides, carbonates, nitrates, borates, sulfates, chromates, phosphates, arsenates, vanadates, tungstates, molybdates, and silicates. Some of these chemical groups have subcategories, which may be categorized in some mineral references as separate groups.

Nine Classes Of Minerals

Geologists have identified over 3000 minerals. In order to study them more closely, they have divided minerals into nine different groups. Table 9-1 shows the broad groupings that minerals have been given.

Table 9-1 Major mineral groups are determined by chemical composition.

Type

Chemical structure

1

Elements

2

Sul.des

3

Halides

4

Oxides and hydroxides

5

Nitrates, carbonates, borates

6

Sulfates

7

Chromates, molybdates, tungstates

8

Phosphates, arsenates, vanadates

9

Silicates

 

Most rocks are composed of minerals . Minerals occur naturally as inorganic solids with a crystalline structure and distinct chemical make up. Table 9-2 gives you an idea of these different compounds. Minerals found in the rocks of the Earth are an assorted combination of different chemical elements. The most common elements that make up the minerals found in the Earth’s rocks are illustrated in Fig. 9-1.

Table 9-2 Minerals are divided by different groupings.

Mineral

Group (element-e, halide-h, oxide-o, silicate-si, sulfide-su, phosphate-p, molybdate-m, borate-b, carbonate-c)

Hardness (Mohs’ scale)

Chemical composition

Antimony

e

3–3.5

Sb

Arsenic

e

3.5

As

Bismuth

e

2–2.5

Bi

Carbon (diamond and graphite)

e

Graphite 1–2 Diamond 10

C

Copper

e

2.5–3

Cu

Gold

e

2.5–3

Au

Nickel–iron

e

4–5

Ni,Fe

Platinum

e

4–4.5

Pt

Silver

e

2.5–3

Ag

Sulfur

e

1.5–2.5

S

Fluorite

h

4

CaF 2

Halite

h

2.5

NaCl

Corundum

o

9

Al 2 O 3 (ruby, sapphire)

Cuprite

o

3.5–4

Cu 2 O

Hematite

o

5–6

Fe 2 O 3

Albite

si

6–6.5

NaAlSi 3 O 8

Anorthite

si

6–6.5

CaAl 2 Si 2 O 8

Beryl

si

7–8

Be 3 Al 2 (SiO 3 ) 6

Dioptase

si

5

CuSiO 2 (OH) 2

Jadeite

si

6–7

Na(Al,Fe +3 )Si 2 O 6

Labradorite

si

6–6.5

(Na,Ca)Al 1–2 Si 3–2 O 8

Microcline

si

6–6.5

KAlSi 3 O 8

Olivine

si

6.5–7

(Mg,Fe) 2 SiO 4

Orthoclase

si

6–6.5

KAlSi 3 O 8

Quartz

si

2.65

SiO 2

Topaz

si

8

Al 2 SiO 4 (F,OH) 2

Zircon

si

7.5

ZrSiO 4

Cinnabar

su

2–2.5

HgS

Galena

su

2.5

PBS

Pyrite

su

6–6.5

FeS 2

Molybdenite

su

1–1.5

MoS 2

Gypsum

su

2

CaSO 4 - 2(H 2 O)

Lazulite

p

5.5–6

(Mg,Fe)Al 2 (PO 4 ) 2 (OH) 2

Turquoise

p

5–6

CuAl 6 (PO 4 ) 4 (OH) 8 ·4H 2 O

Wulfenite

m

2.5–3

PbMoO 4

Borax

b

2–2.5

Na 2 B 4 O 5 (OH) 4 · 8H 2 O

Calcite

c

3

CaCO 3

Malachite

c

3.5–4

Cu 2 (CO 3 )(OH) 2

Rhodochrosite

c

3.5–4

MnCO 3

 

 

Minerals and Gems

Fig. 9-1. Earth minerals are composed of different elements.

Practice problems of this concept can be found at: Minerals and Gems Practice Test

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