identifying minerals
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Identifying Minerals. Mineral Identification. Geologist test physical and chemical properties to identify minerals Color Luster Texture Streak Hardness Cleavage and Fracture Density and Specific Gravity Special Properties. Color. - PowerPoint PPT PresentationTRANSCRIPT
IDENTIFYING MINERALS
Mineral Identification Geologist test physical and chemical
properties to identify minerals Color Luster Texture Streak Hardness Cleavage and Fracture Density and Specific Gravity Special Properties
Color A mineral’s color is a result of chemical
composition and presence of trace elements
Many minerals can be found in more than one color or shade
Example – Quartz can be found in several different forms
Jasper Has traces of iron oxides giving it a red
tinge
Amethyst Contains ferric iron making it purple
Citrine Contains iron hydrates making them
orange
Rose Quartz Contains manganese or titanium
Color is the most obvious characteristic of a mineral but it is also the least reliable.
Luster How the surface of a mineral reflects
light Two main categories
Metallic – mineral shines like chrome Nonmetallic – minerals do not shine
More specific type of nonmetallic Dull Pearly Waxy Silky
Texture How a mineral feels to the touch
Smooth Rough Ragged Greasy Soapy Glassy Texture test is perhaps the most subjective
Streak The color of the mineral in powder form Tested by rubbing the mineral across an
unglazed Streak color is not always the same as
the mineral color in rock form Example – pyrite is gold in rock form but
has a greenish-black streak
Streak cont. Different variations of a mineral have the
same streak Example – Flourite can be purple, yellow,
green, or blue but the streak is always white
When can this test not be used? When the minerals are harder than a
porcelain plate
Hardness A measure of how easily a mineral can
be scratched. Measured on the Moh’s Hardness Scale
One of the best identification tests 1-10 scale: Talc is the softest, diamond is
the hardest Common objects can be used to measure
hardness
Mineral Moh’s Scale Hardness
Hardness of Common Object
Talc 1 (softest)Gypsum 2 Fingernail (2.5)Calcite 3 Piece of copper
(3.5)Flourite 4 Iron nail (4.5)Apatite 5 Glass (5.5)Feldspar 6 Steel file (6.5)Quartz 7 Streak plate (7)Topaz 8 Scratches quartzCorundum 9 Scratches topazDiamond 10 (Hardest) Scratches all
common materials
Cleavage and Fracture Both describe how a mineral breaks
Cleavage – splits easily and evenly along flat planes Mica
Fracture – breaks with rough, jagged edges Quartz
Density and Specific Gravity Density
Very good identification tool Mass divided by volume Density is different than weight
Consider two different amounts of the same mineral
Their weights would be different Their densities would be equal
Specific Gravity Ratio of the weight of a substance to the
weight of an equal volume of water at 4° C
Special Properties Some minerals have unique physical and
chemical properties Double Refraction – light bends in two directions
when it passes through the mineral Magnetism – mineral is naturally magnetic
magnetite Odor – sulfide produces a rotten-egg smell when
rubbed on streak plate Fizzes – chemical reaction to acid or other solutions
Calcite and hydrochloric acid Taste
ORES AND GEMS
Ores A useful mineral can be mined for a
profit Examples
Hematite – source of iron Bauxite – source of aluminum Rutile – source of titanium
Gems Are nothing more than minerals that are
valuable simply because they are prized for their rarity and beauty Examples – Diamonds, Rubies, Amethyst