Rocks & Minerals A mineral is:
Naturally occurring Inorganic
Definite chemical composition & crystalline structure
Solid
All physical properties of minerals come from the “internal arrangement of atoms”
Mineral Identification Tests
The Color Test- easiest test to do but not always reliable 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 shine
the only way to really learn the different lusters is to see them for yourself.
Types of Luster
Metallic- looks like shiney metal
Non-metallic- all the other ways that a mineral can shine
o Glassy/vitreous- shines like a piece of broken glass
(most common non-metallic)
o Dull/earthy- no shine at all
o Resinous/waxy- looks like a piece of plastic or dried
glue
oil slick on water. Also looks like the inside of some clam shells
o 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.
Moh’s Scale of Hardness 1. Talc (Softest)
2. Gypsum
3. Calcite
4. Fluorite
5. Apatite
6. Feldspar (AKA Albite)
7. Quartz
8. Topaz
9. Corundum
10. Diamond (Hardest)
Key Points of a Hardness Test
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
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
Fracture -The way a mineral without cleavage breaks. Examples of Fracture
conchoidal- to break in a scooped out bowl shape- like a conch (sea snail)
hackly fracture- to have irregular sharp edges splintery- to break into long, thin needles Miscellaneous Tests
Acid- Calcite and powdered dolomite will effervesce (fizz) in dilute hydrochloric acid (HCl)
Magnetism- Magnetite (AKA Lodestone) will pick up paper clips (weak samples will only be able to pick up staples)
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.
Double refraction- some clear forms of calcite (Iceland Spar) will make a double image of words.
A little about Quartz:
One of the most abundant minerals in the world (Quartz and feldspar fight for #1)
Makes beach sand
Makes glass (melted beach sand)
Chemical formula: SiO2
Since it is SiO2, there is twice as much oxygen as silicon.
According to the Reference Tables pg 11, 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”
o Tetra = 4
Rocks
A rock is a mixture of one or more minerals. They are classified by the way that they are made.
Monominerallic- a rock made of only one mineral. In this case, the rock is both a rock and a mineral.
Igneous Rocks
“Fire Formed”- melted rock material cools and solidifies (“freezing”)
Intrusive- rock formed inside the Earth Extrusive- rock formed on the surface
Texture- the size of the crystals- NOT HOW IT FEELS
INtrusive Extrusive
Rocks INSIDE the Earth Rocks OUTSIDE the Earth
Plutonic Volcanic
Formed from magma Formed from lava Usually dark Usually light colored Usually dense Usually low density (light) Mafic: (magnesium and Iron (Fe) Felsic: feldspar (aluminum) Cools slowly Cools quickly
Large grains Small or no grains (fine or glassy)
Igneous rocks have “Intergrown Crystals”
Intergrown...
Sedimentary Rocks- Made from sediments or rock material that has been broken down in some way.
Sedimentary rocks are usually formed in a watery environment.
Often layered
Are the only rocks that normally contain fossils
Types of Sedimentary Rocks
Clastic (fragmental) –made by compaction and cementation of sediments.
o Clastic rocks are identified by the size of the fragments.
o Breccia has angular fragments...
Chemically formed rocks: evaporites
o Formed when water carrying minerals evaporates and
leaves the minerals behind.
o Are identified by the minerals present (ie halite
hardness of 2.5)
Bioclastic-
o bio= life
Made from accumulated shells (limestone) or plants (coal)
Metamorphic Rocks
changed from a pre-existing rock
caused by extreme heat and/or pressure
may result in a distorted structure like this...
or this...
Regional Metamorphism
Caused by extreme pressure and heat. Happens over wide “regions”.
To this...
Contact Metamorphism
Caused by contact with extreme heat.
Metamorphic rocks will often have foliation or a distorted structure.
Foliation is a “grain” to the rock. Gneissic Foliation
Banding vs. Layers:
Bands do not go all the way through and across your rock. Layers, like in sedimentary rocks go all the way through like a layer in a cake.
Bands...
Schistose foliation- minerals have been squashed into flakes of mica.
