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The diagram in the next slide represents the ROCK
CYCLE—a scheme that represents the processes of
continuous changes that connect the three major groups of
It also shows two other important parts of the “Rock Cycle”
– SEDIMENTS and molten LAVA and MAGMA
Note about image sources: Many images come from a website (Volcano World) that no
longer is supported, so no credit is given. The last slide provides possible sources.
 A mineral is
 Naturally occurring
 Inorganic
 Definite chemical composition & crystalline structure
 Solid
 All physical properties of minerals come
from the “internal arrangement of atoms”
 The Color Test- easiest test to do but not always
 The Streak Test -The color of the powdered mineral.
 Performed by rubbing the unknown mineral on an
unglazed tile.
 The Luster Test -the way a mineral shines or doesn't
 the only way to really learn the different lusters is to see
them for yourself.
 Metallic- looks like shiny metal
 Non-metallic- all the other ways that a mineral can
 Glassy/vitreous- shines like a piece of broken glass
(most common non-metallic)
Dull/earthy- no shine at all
Resinous/waxy- looks like a piece of plastic or dried glue
Pearly- looks oily it may have a slight rainbow like an oil
slick on water. Also looks like the inside of some clam
Adamantine- brilliant, sparkling shine like a diamond
 Hardness- a minerals resistance to scratching. This
should not be confused with brittleness. A diamond is
very hard and will scratch a hammer but a hammer
will smash a diamond. Likewise, talc, one of the softest
minerals, is not squishy. It will still put a serious
hurting on you if you get hit in the head with it.
 1. Talc (Softest)
 2. Gypsum
 3. Calcite
 4. Fluorite
 5. Apatite
 6. Feldspar (AKA Albite)
 7. Quartz
 8. Topaz
 9. Corundum
 10. Diamond (Hardest)
 Choose one mineral to be the scratcher and one to be the scratchee.
 Pick a smooth, flat surface to scratch.
 After doing the test, wipe the powder away to confirm that the
scratchee really got scratched.
 If the scratchee did not get scratched, switch the two rocks and repeat.
 Hardness Tools
 Fingernail 2.5
 Penny 3.5
 Iron Nail 4.5
 Glass Plate 5.5
 Steel File 6.5
 Streak Plate 7
 Cleavage -To break along flat surfaces.
 Examples of Cleavage
 Cubic- To break into cubes
 Rhombihedral- to break into “pushed over cubes”
 Basal- to split into thin sheets
 The way a mineral
without cleavage breaks.
 Examples of Fracture
 conchoidal- to break in
a scooped out bowl
shape- like a conch (sea
 hackly fracture- to have
irregular sharp edges
 splintery- to break into
long, thin needles
 Acid- Calcite and powdered dolomite will effervesce (fizz)
in dilute hydrochloric acid (HCl)
Smell- Sphalerite will give off a rotten-egg smell when
streaked on a streak plate. (Note: pure sulfur does not smell
like rotten eggs!)
Magnetism- Magnetite (AKA Lodestone) will pick up
paper clips (weak samples will only be able to pick up
Taste- Halite is rock salt and will taste salty. *Do not taste
the samples since some have been tested with acid to
see if it is calcite.
Fluorescence- some minerals (mostly forms of calcite)
will glow in fluorescent colors under a black (UV) light.
 Form by solidification (crystallization) of melted
 At the surface, LAVA hardens to form EXTRUSIVE
rocks with tiny (FINE-GRAINED) crystals or GLASSY
(no crystal) TEXTURES
 Beneath the surface, MAGMA hardens to form
INTRUSIVE rocks with easily visible (COARSEGRAINED) crystal texture.
 Light-colored, coarse-
grained, no pattern
 Mostly quartz,
feldspar, mica, and
 Often used for
buildings and
 Dark-colored, fine-
grained, extrusive
 Formed where lava erupted
onto surface
 Most widespread igneous
 Found locally in the
Palisades along west shore
of Hudson River,
Connecticut River valley
 Dark-colored, coarse-
grained intrusive
 Similar composition to
feldspar with some
pyroxene and olivine
 Natural volcanic glass
 Forms when lava cools
very quickly
 Usually dark, but small
pieces may be clear
 Fractures along curved
(conchoidal) surface
 Used as spear and arrow
points, knives
 Light colored, frothy
(many air spaces)
 Same minerals as in
granite, but finer in grain
Sedimentary rocks may be made of rock fragments—
sediments—or by chemical reactions. The classification of
sediments is shown below.
 The most important of
these is coal. Anthracite
coal results from the
greatest pressure and
releases the most energy
when burned. Other
varieties are bituminous
and lignite. “Petrified”
(permineralized) wood
is another organic rock.
 Shale is the most
common sedimentary
 Sedimentary rocks
cover about threequarters of the land
 For more about
sedimentary rocks:
 Formed by heat and pressure changing existing rocks
 REGIONAL METAMORPHIC affects a large area and
results from plate tectonics
 CONTACT METAMORPHISM affects rocks on a local
scale, such as “baking” sedimentary rocks next to
magma or lava
Gneisses and schists are common in New York City and
 One of the most abundant minerals in the world (Quartz
and feldspar fight for #1)
Makes beach sand
Makes glass (melted beach sand)- Sweet Home Alabama
Chemical formula: SiO2
Since it is SiO2, there is twice as much oxygen as silicon.
Oxygen is the #1 element in the crust with Silicon #2 (and
about half that of Oxygen)
Crystal shape is a pyramid called a “tetrahedron”
 Tetra = 4
 hedron =“sided solid
There are many web sites that can provide you with
more information about rocks and images. Here are a
Dr. Michael J. Passow