THE CASE OF THE
SCARLETT STREAK:
MINERAL IDENTIFICATION
Virginia T. McLemore
New Mexico Bureau of Geology
and Mineral Resources
New Mexico Tech
What is a mineral?
What is a mineral?
•
•
•
•
•
•
naturally occurring
inorganic
solid
homogeneous
crystalline material
with a unique chemical element or
compound with a set chemical formula
• usually obtained from the ground
A crystal is composed of a structural unit that is
repeated in three dimensions. This is the basic
structural unit of a crystal of sodium chloride, the
mineral halite.
Why are minerals important?
Why are minerals important?
• Identification of rocks
• commodities that we use every day
• foundation of understanding geology
and geologic processes that affect us
everyday
• understanding geologic hazards
NEW MEXICO MINING: WHERE
ARE THE DEPOSITS?
New Mexico is at the edge of one of the world’s greatest
metal-bearing provinces
Active mines in New Mexico 2002-2005 (excluding aggregates)
Active aggregate mines in New Mexico.
Stone House zeolite mine,
Sierra County (18.3 million
tons of reserves).
Metals districts with Significant deposits in New Mexico
Minerals have distinctive
physical and chemical
properties that allow for their
identification.
Properties of minerals
 Habit (Crystal
forms and
shapes)
 Hardness
 Cleavage
 Streak
 Color
 Luster
 Transparency
 Twinning
 Fracture
 Specific Gravity
 Associated
Minerals
 Fluorescence
 Magnetism
 Odor
 Feel
 Taste
 Solubility
 Reaction to acids
 Radioactive
minerals
 Meteoritic
minerals
Hardness
• ease or difficulty with
which the mineral can be
scratched
• controlled by the strength
of bonds between atoms
Hardness
Cleavage
• Way the mineral
breaks or fractures
• one direction of
weakness, or in
other minerals, 2, 3,
4, or as many as 6
may be present
Cleavage
• determine the
angular relation
between the
resulting cleavage
surfaces
– perpendicular
– acute
– obtuse
www.ironorchid.com/minerals/
From:geology.csupomona.edu/alert/mineral/minerals.htm
Streak
Streak
• color of a mineral
when it is powdered
• crushing and
powdering a mineral
eliminates some of
the effects of
impurities and
structural flaws
•
•
•
•
•
•
Black - Graphite
Black - Pyrite
Black - Magnetite
Black - Chalcopyrite
Gray - Galena
Limonite - Yellowbrown
• Hematite - Redbrown
From:geology.csupomona.edu/alert/mineral/minerals.htm
academic.brooklyn.cuny.edu/geology/leveson/core/linksa/mineral_id...
Luster
• way a mineral’s
surface reflects light
Luster
•
•
•
•
•
•
metallic
earthy
waxy
greasy
vitreous (glassy)
adamantine (or
brilliant, as in a
faceted diamond)
From:geology.csupomona.edu/alert/mineral/minerals.htm
www.ironorchid.com/minerals/
Properties of minerals
 Habit (Crystal
forms and
shapes)
 Hardness
 Cleavage
 Streak
 Color
 Luster
 Transparency
 Twinning
 Fracture
 Specific Gravity
 Associated
Minerals
 Fluorescence
 Magnetism
 Odor
 Feel
 Taste
 Solubility
 Reaction to acids
 Radioactive
minerals
 Meteoritic
minerals
Color
From:geology.csupomona.edu/alert/mineral/minerals.htm
• Crystal shape
• six crystal systems
• governed by the
mineral's internal
structure
Habit
•
•
•
•
•
•
triclinic
monoclinic
orthorhombic
tetragonal
hexagonal
isometric
From:geology.csupomona.edu/alert/mineral/
minerals.htm
Specific Gravity
• specific gravity
– ratio of mineral density to the density
of water
• similar to weight
• density
– ratio of the mass of a mineral to its volume
academic.brooklyn.cuny.edu/geology/lev
eson/core/linksa/mineral_id...
academic.brooklyn.cuny.edu/geology/leveson/core/linksa/mineral_id...