Which of these is a mineral (if not, why not)

• Coal
• Obsidian
• Metal in an iron meteorite (kamacite, taenite)
• Apatite (solid material found in your teeth, bones)
• Calcite in the shell of a clam
• Calcite dissolved and re-precipitated
• A glacier
• Clay stuck to my shoes
• Gold
• Fool’s Gold
MINERAL IDENTIFICATION
Luster

Cleavage / fracture
Crystal form
Density (specific gravity) Hardness
Color
SILICATE MINERALS
¡ Composed of silica tetrahedra (SiO4)
¡ Found mostly in igneous rocks

Fig. 3.13, p. 73
Review
• What was the most abundant element in the Earth’s
crust?

• What was second?

Mineral Groups

• Oxides – simple, one element surrounded by oxygen

• Silicates – Have Silicon-Oxygen bonds in them
• Carbonates – Carbon-oxygen bonds in them
• Native elements - made of a single element
• Sulfides – Backbone of sulfur
• Sulfates – Backbone of Sulfate (SO4)
• Halides – Bonded with F, Cl, etc.
 Common Silicate Minerals

• Silicates are the most abundant group of minerals in Earth.

• Make up 92% of the Earth’s mantle and crust.
• Silicates are subdivided into light (non-ferromagnesian) and dark
(ferromagnesian) groups.
• Light ones: Feldspar + Silica = FELSIC
• The feldspars are the most common silicate group and make up more than
50% of Earth’s crust.
• Quartz is the second-most abundant mineral in the continental crust and the
only common mineral made completely of silicon and oxygen.
• Dark minerals include olivine, garnet, pyroxenes, and they make up
much of the Earth’s mantle.
• Have lots of iron and magnesium in them - Mafic
SILICATE MINERALS
¡ Ferromagnesian silicates – contain iron (Fe), magnesium (Mg), or both
combined with other elements
¡ mafic = magnesium (ma) + iron (ferric)

amphibole

olivine
pyroxene biotite

Fig. 3.13, p. 73
 Pyroxene and Hornblende
Mafic minerals tend to be dark, due to the
presence of iron.
 Common Silicate Minerals

• The Light Silicates

• Quartz
• Only common silicate composed entirely of
oxygen and silicon
• Hard and resistant to weathering
• Fractures into sharp shards
• Often forms hexagonal crystals
• Colored by impurities (various ions)
• Muscovite
• Common member of the mica family
• Forms thin sheets
• Used as “glass” during the Middle Ages
• Produces the “glimmering” brilliance often
seen in beach sand
Common Silicate Minerals
Common Silicate Minerals
 Common Silicate Minerals

• The Light Silicates

• Clay minerals
• “Clay” is a general term used to describe a variety of complex fine-grained
minerals that have sheet structure.
• Clay makes up a large percentage of soil
• Have a lot of water (hydrogen) stuck in their structure
• Kaolinite is common clay mineral with a huge number of uses
 Important Nonsilicate Minerals

• Carbonates
• Composed of the carbonate ion (CO32−) and a positive ion
• Two most common carbonates are calcite (CaCO3) and
dolomite CaMg(CO3)2
• Primary constituents in limestone and dolostone
• Used as road aggregate, building stone, and main ingredient
in Portland cement.
C ARBONATE MINERALS
¡ All carbonate minerals have carbonate (CO³)-² as in calcite, CaCO³,
and dolomite, CaMg(CO³)².
¡ Carbonate minerals are mostly found in the sedimentary rocks
limestone and dolostone.
¡ Carbonates are derived from the shells and hard parts of marine
organisms or are precipitated from seawater as evaporites
OTHER MINERAL GROUPS
¡ Native elements
¡ Composed of a single
element
¡ Gold, copper, graphite, and
diamonds commonly occur
as native elements

Geo-inSight 6., p. 73
OTHER MINERAL GROUPS
¡ Sulfides - sulfur, no oxygen
¡ All sulfide minerals contain sulfur plus a metallic element, as in
galena (PbS) and pyrite (FeS2).

galena pyrite
OTHER MINERAL GROUPS
¡ Sulfates – all sulfate minerals contain
sulfate (SO4-2), as in gypsum
(CaSO4•2H2O).
¡ Halides – all halide minerals contain a
halogen atom (F, Cl, etc.), as in halite
(NaCl).
¡ Sulfate and halide minerals are common in
deserts, forming from evaporation of
water (also called evaporites).
GRAPHITE VS. DIAMOND
¡ What makes graphite different from diamond?

TIME & PRESSURE

Cr ystal
structu
re and b
differen o nds ma
ce! ke a
Sheets
connected Framework
with weak of strong
Van der covalent
Waals bonds bonds
Given an unknown mineral, how do you
identify it?
Certain properties of minerals can be used to
narrow down and Identify what a mineral is.
• Cleavage • Streak
• Crystal habit/form • Density/Specific Gravity
• Fracture • Taste
• Hardness • Feel
• Luster • Magnetism
• Color • Effervescence
Properties of Minerals - Cleavage
Properties of Minerals
Properties of Minerals
 Properties of Minerals

• Mineral Strength
• How easily minerals break or deform under stress
• Hardness
• What can scratch what?
• All minerals are compared to a standard scale called the Mohs scale of hardness.
• Is a measurement of how strong chemical bonds are.
https://www.nps.gov/articles/mohs-hardness-scale.htm
 Submetallic and Metallic Luster of Galena
(PbS)
Luster refers to how a material reflects light. There are different degrees of Luster, but
usually I use “Metallic” for things that look like metals and non-metallic for things that
look rocky.
Color Variations in Minerals
How many different minerals are shown here?
 Properties of Minerals

• Optical Properties
• Streak
• Color of a mineral in its powdered form
• Obtained by rubbing mineral across a porcelain streak plate.
• Not every mineral produces a streak when rubbed across a streak plate.
• Although a mineral’s color may vary, its streak is usually consistent in color.
Streak is powdered material created by grinding a
crystal on a porcelain plate.

https://geology.cochise.edu/mineral/pyrite-82/
 Properties of Minerals

• Density and Specific Gravity

• Density is defined as mass per unit volume
• Specific gravity is a related measure and more frequently used by
mineralogists
• The ratio of the weight of a mineral to the weight of an equal volume of water
• Most have a specific gravity between 2 and 3
• Metallic minerals can have more than twice that specific gravity
• The specific gravity of galena (PbS) is 7.5 and 24 karat gold is 20!
Properties of Minerals

• Other Properties of Minerals:

• Taste
• Halite tastes like salt
• Feel
• Talc feels soapy, graphite feels greasy
• Stinky streak
• Sulfur-bearing minerals have streaks that smell like rotten eggs
• Magnetism
• Magnets pick up magnetite, lodestone is a natural magnet
• Double refraction
• Transparent calcite
• Effervescence
• Carbonates fizz in reaction to dilute hydrochloric acid
Properties of Minerals
Properties of Minerals
How do you identify minerals
• You can’t use just one property
• You have to often test 3 or 4 things.
• You recognize color immediately, but it sometimes doesn’t help, sometimes flat
out lies.
• Sometimes color can be useful
• Check the luster.
• Test the hardness.
• Check the shape, cleavage if possible.
• Check the density
• Check: minor properties (effervescence)
• All or nearly all things should agree. If everything says “Quartz” but you can
scratch it with your fingernail, its not quartz.
HOW DO MINERALS FORM?
¡ As molten rock
(magma – lava at the
surface) cools, minerals
crystallize and grow

¡ Minerals also precipitate

from evaporating
water

¡ Some minerals form in

hydrothermal
systems
ROCKS
IGNEOUS
ROCKS
MINERALS IN IGNEOUS ROCKS

Ultramafic Mafic Intermediate Felsic

dark and/or green light-colored

dense light-weight
iron- / magnesium-rich silica-rich
form at high temperatures low temperatures
COMPOSITION OF MAGMA
Sodium,
Magma Silica Calcium, iron,
potassium, and
composition content (%) and magnesium
aluminum
Ultramafic <45 Increase
Mafic 45-52
Intermediate 53-65
Felsic Increase >65 Increase
MAGMA VISCOSITY AND COMPOSITIONS
Ultramafic

viscosity
temperature

Mafic

Intermediate

Felsic
IGNEOUS ROCKS! COMPOSITION
§ Ultramafic rocks
§ Peridotite is an ultramafic rock,
meaning that it is high in magnesium and iron.
https://commons.wikimedia.org/wiki/File:Peridotite_mantle_xenolith_in_vesicular_phonotephrite_

§ Its composition is close to that of %28Peridot_Mesa_Flow,_Middle_Pleistocene,_580_ka;_Peridot_Mesa,_San_Carlos_Volcanic_

Field,_Arizona%29_8_%2831130713391%29.jpg

the upper mantle.

§ Mafic rocks
§ Basalt is the most common mafic rock
§ It forms the crust of many planets, including
the Earth’s ocean.

https://www.flickr.com/photos/jsjgeology/16540710327
MAGMA FORMATION AT SPREADING RIDGES
§ At mid-ocean ridges melting of the mantle forms the mafic
magmas that create the oceanic crust
Ocean floor formation – pillow lavas
MAGMA FORMATION IN HOT SPOTS
§ Hot spot activity generates mafic magmas
§ Originate in lower mantle
§ Rising plumes into ocean crusts create volcanic islands
§ On the continents, flood basalts result
MAGMAS FORMATION IN SUBDUCTION ZONES
§ Along subduction zones at convergent boundaries, partial melting
of the subducting plate produces intermediate to felsic magmas.
Intermediate to Felsic

Fine grained intermediate rock is an Andesite

Fine grained felsic rock is a rhyolite
https://www.flickr.com/photos/jsjgeology/26612224237 https://www.flickr.com/photos/jsjgeology/51645682736
IGNEOUS ROCKS! COMPOSITION
§ Take a look at the rock. Is it light or dark?
§ Gives you hints about its composition!
§ Which composition is each of the below rocks?

Mafic Intermediate Felsic

IGNEOUS ROCKS! TEXTURES
§ Size, shape, and arrangement of grains (crystals) in a rock.
§ Minerals begin to crystallize from magma and lava after small crystal nuclei
form and grow.
§ Which cooled slower of the two rocks below? Why?
IGNEOUS ROCKS! TEXTURES
§ Grain size growth is like anything else that grows (people, plants,
animals, etc.): given more time, it grows bigger.

§ Rapid cooling from erupting out of a volcano or

cooling just under the surface doesn’t allow grains
much time to grow, resulting in a fine-grained rock

§ Slow cooling underground with the surrounding rock

acting as an insulator allows grains to grow large over
a long time, resulting in a coarse-grained rock
IGNEOUS ROCKS! TEXTURES
§ Two broad groups based on texture:

§ Extrusive rocks extrude or erupt from the crust (they get out)
§ They have a fine-grained aphanitic texture.

§ Intrusive rocks intrude into the crust (and stay there)

§ They have a coarser-grained phaneritic texture

§ Rocks with more complex cooling histories are

characterized by porphyritic textures.
IGNEOUS ROCKS! TEXTURES
§ Porphyritic texture: complex
cooling history (e.g., slow cooling,
then fast) = contains mineral
grains of different sizes.

§ Occurs when a rock begins

cooling slowly underground,
forming the large grains, and is
then erupted, forming the fine-
grained matrix between the large
grains
IGNEOUS ROCKS! TEXTURES
Very slow cooling
Name these

Slow cooling
cooling speeds!
Add a textural
term.

Slow then fast

Fast cooling
IGNEOUS ROCKS! COMPOSITION
§ Igneous rocks of the same chemically compositions can be intrusive or
extrusive rocks.
§ Because one is intrusive and one is extrusive, they will have different
textures and appearances, even though they are made of the same
magma composition
IGNEOUS ROCKS! COMPOSITION
§ Mafic rocks
§ Basalt and gabbro are chemically equivalent mafic rocks.

§ Basalt is an extrusive rock. Gabbro is an intrusive rock.

IGNEOUS ROCKS! COMPOSITION
§ Intermediate rocks
§ Andesite and diorite are chemically equivalent intermediate rocks.

§ Andesite is an extrusive rock. Diorite is an intrusive rock.

IGNEOUS ROCKS! COMPOSITION
§ Felsic rocks
§ Rhyolite and granite are chemically equivalent felsic rocks.

§ Rhyolite is an extrusive rock. Granite is an intrusive rock.

IGNEOUS ROCKS! TEXTURES
§ Other igneous rock textures:
§ Vesicular – with holes (vesicles)
§ indicates the rock formed as water vapor and other gases
became trapped during cooling
of lava
§ Pyroclastic
§ contains fragments formed by consolidation
of volcanic ash or other pyroclastic material
§ Glassy
§ no grains – cooled too quickly for minerals to grow

These textures all occur from

rapid cooling on the surface
OTHER IGNEOUS ROCKS…
§ Obsidian
§ Shiny volcanic glass that is normally grey to black
§ Equivalent composition to rhyolite and granite – felsic!
§ Cools too quickly to form crystals
OTHER IGNEOUS ROCKS…
§ Tuff (welded and non-welded)
§ Volcanic rock composed of a mix of volcanic ash, pumice, crystals, and
rock fragments
§ Welded tuff: particles buried while still hot (in the pyroclastic flow) – ash
melted together, feels much more solid
§ Non-welded tuff: particles cooled before being buried (settled out from
the eruption column) – compacted ash, feels like chalk
WHY DO WE CARE ABOUT IGNEOUS ROCKS
§ Building stones (dimension stone)
§ Many igneous rocks are useful in building things.
WHY DO WE CARE ABOUT IGNEOUS ROCKS
§ Resources
§ Many igneous rocks are the sources of resources.

https://www.usgs.gov/media/images/fine-
grained-massive-sulfide-0
WHY DO WE CARE ABOUT IGNEOUS ROCKS
§ Age dating
§ Igneous rocks are the rocks we can use for age dating/measurements.

https://www.nps.gov/subjects/geology/ign
eous.htm
SEDIMENTARY
ROCKS