Identification

Minerals have physical properties that can be used to identify them

1. Crystals - atoms that make up the mineral of a crystal are arranged in a repeating pattern. Some crystals have smooth growth surfaces called crystal faces (pyrite commonly has 6 crystal faces)
2. Cleavage - (the way it breaks) Minerals that split or break along a smooth surface into pieces with smooth regular planes and reflect light are said to have cleavage. It's like peeling off a piece of pre-sliced cheese. This is caused by weaknesses in the arrangement of atoms (^ex mica)
3. Fracture - (the way it breaks) Minerals that break into pieces with jagged or rough edges have fracture. These are not neat slices, more like hunks of cheese. (^ex quartz)
4. Color - color can help identify a mineral but may not be used as the only indicator.
5. Streak - scraping a mineral across an unglazed white tile called a streak plate produces a streak of color from the powdered mineral. The streak may not be the same color as the original mineral piece, but it is the true color of the mineral.
6. Luster - describes how light reflects from a mineral's surface (shiny, dull, pearly). If it shines like a metal the mineral has metallic luster. Non-metallic minerals can be described as having pearly, glassy, dull, or earthy luster.
7. Hardness - some minerals are harder than others. Some can be scratched with a fingernail, while others can cut through glass (diamond). The Moh's Scale is used to classify minerals by their hardness. 1=the softest (Talc) to 10= the hardest (diamond). You can use mineral identification kits, which contain a nail, penny, and a glass plate, to help determine the hardness of a mineral.
8. Specific Gravity - some minerals are heavier for their size than others. Specific gravity compares the weight of a mineral to the weight of an equal volume of water.
9. Other Properties
   1. Magnetite - will attract magnets (magnetic)
   2. Calcite - fizzes when in the presence of hydrochloric acid (HCL). Also, if you look through clear crystal, you will see a double image.
   3. Halite - is salty (rock salt). Some scientists use their sense of taste to identify a mineral, but for classroom purposes, I don't suggest it. : )

Rocks are made up of two or more minerals. There are 3 different types of rocks: Igneous, Sedimentary, and Metamorphic

Igneous Rocks

The deeper you go into Earth, the higher the temperature and the greater the pressure. Igneous rock forms when melted rock material from inside Earth cools. When melted rock material cools on Earths surface (lava) it makes extrusive igneous rock. When it cools below Earth's surface (magma), it makes an intrusive igneous rock.

The chemicals in the melted rock determine the color of the rock. If it contains a high level of silica, the rock will be light in color. These are called granitic rocks. Intrusive igneous rocks are often granitic rocks. If it contains a high level or iron, magnesium, or calcium, a dark colored or basaltic rock will form. Extrusive igneous rocks are often basaltic.

Rocks from Lava - Extrusive igneous rocks

• Rocks cool quickly before mineral crystals have time to form, therefore these rocks have smooth, sometimes glassy appearance
• They form in 2 ways, volcanoes and fissures
  • Volcanoes erupt and shoot out lava and ash
  • Large cracks in the Earth's crust called fissures open up and lava oozes out onto the ground or water.
• Fastest cooling lava has no grains (obsidian)
• Lava that traps gas, cools to form rocks with many holes (pumice)

Rocks from Magma - Intrusive igneous rocks

• Forms when magma cools below Earth's surface
• When a glob of magma is forced up towards the Earth's surface but can't get out, magma sits there and cools slowly (millions of years)
• This slow cooling allows minerals to form LARGE crystals that are easy to see (granite)

Sedimentary Rocks

Sedimentary rocks are made up of broken rocks, shells, minerals, grains, and other materials (sediments). Sediments collect in layers to form rocks -> SEDIMENTARY ROCKS.

Sediment can be carried by rivers, oceans waves, mudslides, glaciers, and wind. After sediment is dropped or deposited, it starts the process to become a rock (which takes between thousands and millions of years).

Sedimentary rocks fall into 3 main categories: DETRITAL, CHEMICAL, AND ORGANIC.

1. Detrital Rocks – pieces of other rocks. These rocks are made of grains of minerals or other rocks that have been deposited in layers by water, ice, gravity, or wind. The weight of sediment above helps “squeeze” the layers into the rock. Pebbles mixed with sediment and cemented together are called conglomerate rocks. ^Ex// (Sandstone, shale, siltstone, conglomerate)

2. Chemical Rocks – evaporation or other chemical process. These rocks form when sea water, loaded with minerals, evaporates. Also, when mineral rich water from geysers, hot springs, or salty lakes, evaporates leaving layers of minerals. ^EX// (When sea water evaporates on skin, you see salt crystals or halite)

3. Organic Rocks – remains of once living things. These rocks are formed when living matter dies, piles up, and then is compressed into rock. If the rock is produced from layers of plants piled on top of one another it’s called coal. ^Ex// (coal, chalk, limestone)

Metamorphic Rock

Many physical changes in and on the Earth are constantly changing rocks. Low and high temperature conditions and pressures can change the chemistry and grain size of rocks. This often takes place when tectonic plates collide and form mountains. Rocks cooked when magma is forced upward can change the mineral crystals in a rock. It can take millions of years to change a rock.

Metamorphic Rocks

New rocks that form when existing rocks are heated or squeezed but are not melted are called metamorphic rocks. Metamorphic = change of form. This describes how some rock take on a whole new look when they are under great pressures.

(^ex// granite -> gneiss, sandstone -> quartzite, limestone -> marble)

New metamorphic rocks can form from any existing rock (igneous, sedimentary, or metamorphic rocks) A physical characteristic for classifying all rocks is texture. Texture differences in metamorphic rocks divide them into two main rocks: foliated and non-foliated.

1. Foliated = leafy Foliated Rocks have visible layers or elongated grains of minerals. These minerals have been heated or squeezed into parallel layers or “leaves.” Many foliated rocks have bands of different colored minerals. (^EX// slate, gneiss, phyllite, schist)
2. Non-foliated Rocks do not have distinct layers or bands. (^EX// quartzite, marble, soapstone).