Transcript Rocks and Mineral Continuedx

Metamorphic rocks are rocks that have
"morphed" into another kind of rock. These
rocks were once igneous or sedimentary
rocks.
 The rocks are under tons and tons of pressure,
which fosters heat build up, and this causes
them to change underground.
 As a result, most of the thousands of rare
minerals known to science occur in
metamorphic rocks.
 The presence of mineral layers, called
foliation, is important to observe when
identifying a metamorphic rock.
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Schist Parent- Shale or Phyllite
 Gneiss Parent- Granitic and volcanic rocks
 Slate
Parent- Shale
 Phyllite Parent- Mudstones and shale
 Marble Parent- Limestone
 Quartzite Parent- Quartz sandstone
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Physical Properties- Properties used to
visually identify a specific mineral
 Color
 Luster
 Transparency
 Crystal systems
 Cleavage
 Fracture
 Hardness
 Specific Gravity
 Streak
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Color is the first thing someone notices
when they view a mineral. Color is also
one of the big reasons that attract
people to minerals. Color in minerals is
caused by the absorption, or lack of
absorption, of various wavelengths of
light. Many minerals come in different
colors and some minerals' colors are
identical to other minerals' colors.
 Ex. Quartz can come in pink, purple,
white, golden yellow or smoky grey.
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Luster is a description of the way light
interacts with the surface of a crystal.
 Types of Luster- 2 main categories
Metallic - the look of metals (shiny)
Ex. Gold, Silver, Galena, Pyrite
Non-metallic- not shiny
 Ex. Sulfur, Feldspar, Talc
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Adamantine-Clear and Brilliant like a
diamond (most gems)
Dull- a non-reflective surface of any kind
Earthy- the look of dirt or dried mud
Pearly- the look of a pearl
Waxy- the look of wax
Fibrous- the look of fibers
Greasy- the look of grease
Resinous- the look of resins such as dried
glue or chewing gum
Vitreous-the most common luster, it simply
means the look of glass
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Transparent- light enters and exits the
surface of the substance in relatively
undisturbed fashion. Can see all visible light
and can distinguish an object when looking
through it.
Ex. Diamond
Translucent- light enters and exits the
surface of the substance in relatively
undisturbed fashion. Can see light through
it, but can not clearly distinguish an object
while looking through it.
Ex. Quartz
Opaque- If the light can not even
penetrate the surface of the substance.
Ex. Feldspar
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A mineral has flat sides called faces. These
faces are flat and join at different angles. The
joined faces make a certain shape.
Cubic- Crystals grow in the shape of a cube
Tetragonal- square bottom and top face with
a rectangular body.
Orthorhombic- a rectangular prism with a
rectangular base
Monoclinic-They form a rectangular prism with
a parallelogram as its base.
TriclinicHexagonal- face forms a hexagon
Trigonal-similar to a cube that has been
compressed to one side.
› Crystal cleavage is a smooth break
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producing what appears to be a flat crystal
face.
Cleavage is reproducible, meaning that a
crystal can be broken along the same
parallel plane over and over again
All cleavage must parallel
All cleavage planes of a mineral must match
that mineral's crystal system
The same mineral will always, always have
the same cleavage
Cleavage occurs in minerals that have
specific planes of weakness
Ex. Fluorite= Octahedral Cleavage,
Calcite= Rhombohedral, Halite=cubic
The way a Rock Breaks
Types of Fracture
 Conchoidal- smoothly curved fracture that
looks like a piece of chipped or broken glass.
Sometimes described as a clam-shell fracture.
 Ex. Quartz, Obsidian
 Uneven- basically self explanatory, the fracture
does not have a pattern and can not be
identically repeated
 Ex. Anhydrite
 Jagged- has sharp points or edges that catch
on a finger that's rubbed across the surface.
 Ex. Metals such as Copper
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Hardness- measure of the strength of the
structure of the mineral relative to the
strength of its chemical bonds.
Minerals with small atoms, packed tightly
together with strong covalent bonds
throughout tend to be the hardest minerals.
The softest minerals have metallic bonds or
even weaker van der Waals bonds as
important components of their structure
Hardness can be tested through scratching.
A mineral can only be scratched by a
harder substance.
Use Mohs Hardness Scale
Mohs Hardness Scale
1. Talc
2. Gypsum
3. Calcite
4. Fluorite
5. Apatite
6. Orthoclase
7. Quartz
8. Topaz
9. Corundum (ruby and sapphire)
10. Diamond
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Specific Gravity- measure of the density of
a mineral.
Non-metallic minerals tend to be of a low
density
Metallic minerals tend to be of higher
density
HEFTING- To use specific gravity, hold a
mineral of unknown SG in one hand and in
the other hand a mineral of known SG
preferably one near the average of 2.75
and of the same size as the unknown
mineral; then compare.
Ex. Galena vs. Quartz
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Streak is actually the color of the powder of a
mineral.
Streak is closely related to color, but is a
different property because the color of the
mineral may be different than the color of the
streak
The proper way to test for streak is to rub a
mineral across a tile of white unglazed
porcelain and to examine the color of the
"streak" left behind.
Two minerals that have similar outward color
may have different colors when powdered.
Ex. the minerals hematite and galena can be
confused when both have a gray color.
However, hematite's streak is reddish-brown,
while galena's streak is lead gray.
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When two tectonic plates collide one may be
pushed down into the mantle. It heats and
melts
Magma that is made will have different
chemical composition depending on where it
comes from.
Magmas from Continental Crust - rich in silicon
and aluminum
Magmas from oceanic crust - rich in iron and
magnesium
Composition determines which rocks will be
made when magma cools
N.L. Bowen - showed that cooling magmas
produce minerals in a predictable order
 Two sides - Iron (Fe) rich side and a
calcium / sodium (Ca / Na) rich side.
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Magma types
MAFIC
Basalt
Intermediate
Andesite
FELSIC
Rhyolite
Olivine - First Fe rich mineral to form - in
tetrahedra shape - easily weathered on the
surface
 Pyroxenes - Tetrahedra link in long chains also weather easily
 Amphiboles - double strands made from linking
pyroxenes
 Biotite Micas - amphibole chains make sheets
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 Calcium/Sodium
Feldspar - from the
Ca/Na side like olivine but Al is inside
the tetrahedra instead of Silicon
Potassium Feldspars - as temp cools Ca
and Na replace Al inside the
tetrahedron
 Quartz - very low temperatures - little left
in magma except Si and O -three
dimensional networks
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