Page 270 - Ultimate Visual Dictionary (DK)

GEOLOGY, GEOGRAPHY, AND METEOROLOGY

Minerals NATIVE ELEMENTS
Dendritic
(branching)
A MINERAL IS A NATURALLY OCCURRING SUBSTANCE that has a characteristic copper
chemical composition and specific physical properties, such as habit and streak
(see pp. 270-271). A rock, by comparison, is an aggregate of minerals and need
not have a specific chemical composition. Minerals are made up of elements
(substances that cannot be broken down chemically into simpler substances),
each of which can be represented by a chemical symbol. Minerals can be
divided into two main groups: native elements and compounds. Native
elements are made up of a pure element. Examples include gold (chemical
symbol Au), silver (Ag), copper (Cu), and carbon (C); carbon occurs as a native
element in two forms, diamond and graphite. Compounds are combinations of
two or more elements. For example, sulfides are compounds of sulfur (S) and one
or more other elements, such as lead (Pb) in the mineral galena, or antimony (Sb) Limonite
in the mineral stibnite. groundmass
Dendritic COPPER (matrix)
(branching) (Cu)
SULFIDES
gold White
diamond Hexagonal
graphite
Kimberlite crystal
groundmass
(matrix)
Quartz
vein
GOLD DIAMOND GRAPHITE
(Au) (C) (C)

Rounded bauxite
Cubic OXIDES/HYDROXIDES grains in groundmass
galena
(matrix)
crystal
Milky quartz
groundmass Mass of
(matrix) specular
hematite
Smoky crystals
GALENA
(PbS) quartz
crystal
Prismatic SMOKY QUARTZ SPECULAR HEMATITE
stibnite (SiO ) (Fe 2 O 3 )
2
crystal
BAUXITE
(FeO(OH) and Al 2 O 3 .2H 2 O)
Quartz Specular
groundmass Kidney ore crystals of
(matrix) STIBNITE hematite hematite
(Sb S )
2 3
Perfect Quartz
octahedral crystal
pyrites crystal

Parallel
bands of
onyx
PYRITES ONYX KIDNEY ORE HEMATITE
(FeS 2 ) (SiO 2 ) (Fe 2 O 3 )

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