Minerals

  Minerals are inorganic, naturally occurring, homogenous, crystalline substances. – Crystal: A solid substance with atoms

arranged in an orderly, repeating pattern.

• Minerals are compounds of specific elements (See your ESRT)

• A mineral can be composed of one element, [i.e. graphite], or multiple elements, [i.e. hornblende or augite.] (See your ESRT – again!!)

In order for matter to be classified as a mineral, it must meet these 5 requirements:

1. Occur naturally

2. Be a solid

3. Have a definite chemical composition

4. Have atoms arranged in an orderly pattern [crystalline]

5. Be inorganic (not formed from plants, animals, or other living organisms)

• Minerals occur whenever rocks are formed since rocks are actually one or more minerals grouped together to form an aggregate.

• 99% of the Earth's crust is made up of only eight elements. These are, in descending order of volume, oxygen, potassium, sodium, calcium, silicon, aluminum, iron, and magnesium. These same elements make up the majority of minerals. (Hmmm, this might be in your ESRT . . .)

• Most rocks have a number of minerals in common. Six of the most common rock-forming minerals are: mica, olivine, orthoclase [feldspar], plagioclase [feldspar], pyroxene, and quartz.

• Mineral Identification:

Each mineral has certain physical and chemical properties that can be used for identification:

Color• Color is not a good

property to be used in the identification of minerals.

• It can be confusing because some minerals' colors are identical to other minerals' colors. Many minerals have different colors caused by impurities; quartz for example, comes in a myriad of colors

Streak

• Streak is the color of the powder of a mineral.

• It 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 streak is more reliable because it will be constant no matter what impurities may be in the mineral.

Luster• Luster is the appearance

of light reflected off of the surface of a mineral.

• The two main categories of luster are metallic and nonmetallic. Most minerals are non-metallic. (ESRT!)

• A metallic luster shines, like gold or steel [pyrite, galena]

• A non-metallic luster can be dull, glassy [like quartz], or pearly [like hornblende]

Hardness• Hardness is how well a substance will resist scratching by

another substance NOT an indication of how easily a mineral breaks.

• The Mohs Scale is the standard scale to measure hardness. It consists of numbers one through ten; 1 being the softest (talc) and 10 being the hardest (diamond).

• Hardness is determined by comparing minerals to other, known substances using the scale.

• Specific Gravity determines how heavy a mineral is compared to an equal volume of water.

• Water has a specific gravity of 1. If a mineral has a specific gravity of 2.7, it is 2.7 times heavier than water.

• Minerals with a specific gravity under 2 are considered light, between 2 and 4.5 average, and greater than 4.5 heavy.

• Most minerals with a metallic luster are heavy. The specific gravity may vary slightly within a mineral because of impurities present in the mineral.

Cleavage is an indication of how a mineral breaks and a mineral can break in two ways:

1. Cleavage breaks along flat surfaces.

2. Fracture breaks along uneven surfaces and can be demonstrated by irregular, fibrous or curved edges.

• Chemical Properties determine the internal arrangement of a mineral’s ions or atoms and dictate the mineral’s characteristics.

• Diamond (left) and graphite (right) are both composed of 100% carbon; the arrangment of the atoms gives each its unique characteristics.

• A crystal’s microscopic shape [the shape of its internal atoms] will be reflected in its macroscopic shape [the shape we see].

Mineral Identification:• Minerals can be identified by observing the

characteristics discussed. • ID kits contain a streak plate, hand lens, glass

plate, nail, and penny.

• Some minerals can be identified by observing their reaction to an acid test. Calcite, for example, will ‘fizz’ when it comes in contact with acid (check your ESRT).

Mineral ID “Hints”:• Useful properties:

– Hardness

– Cleavage/Fracture

– Specific Gravity

• Not-so Useful Properties:– Color

– Luster

•All minerals are rocks. . .

•. . . but not all rocks are minerals