Mineral

Identification

Field Guide

Field Guide Instructions

Create a field guide (booklet) for identifying minerals. Be sure to follow the directions carefully, and include pictures where appropriate.1. Take 3 sheets of plain paper, fold in half (hamburger), then staple to

create a booklet. 2. On the front cover write the title: Mineral Identification Field Guide,

and your name & block number3. Inside the front cover: write a proper definition for mineral (next

slide, choose the correct answer)4. Write one identification test on each page of the field guide:

• Luster• Density• Color• Cleavage• Fracture

5. On the back cover: List & define each mineral group, include examples.

• Hardness• Crystalline Structure• Streak• Special Properties

•A mineral is…

• a.) a substance that cannot be separated or broken down into simpler substances by chemical reactions.

• b.) a substance made up of atoms of two or more different elements joined by chemical bonds.

• c.) a naturally formed inorganic solid that has a definite crystalline structure .

• d.) a solid whose atoms, ions, or molecules are arranged in a definite pattern.

Review

Luster

Luster refers to the way in which a mineral reflects light from its surface. There are 2 broad luster groups…

1. Metallic: Looks like metal (shiny)2. Non-metallic: Many different types…

Density ~ Some minerals are more dense than others. This means that samples which are about the same size can vary greatly in weight because the atoms inside are heavier or packed more tightly. Density can also be referred to as specific gravity. D = M / V It remains the same (no matter the sample size)

Use a balance, or water displacement to measure

Density

Even though each piece of gold is a different size, they all

have the same density 19.3

Color

Color is an easy test since it only involves observation, however it is not a reliable test because…

The color may change over timeSome minerals have many colors (quartz) due to

impuritiesMany minerals have the same color (gold & pyrite)

?

Cleavage

Cleavage describes how a mineral breaks into flat surfaces (usually one, two, three or four surfaces).

Determined by the crystal structure of the mineral.

Not all minerals will have cleavage Some common cleavage type are

shown on the right & below

Fracture

Fracture describes how a mineral breaks into forms or shapes other than flat surfaces.

Conchoidal: describes a curved, nearly rounded, smooth fracture that looks like the inside of a shell. (obsidian)

Fibrous: minerals (chrysotile asbestos) that break into fibers. Splintery: minerals break into sharp, needle-like pieces. Hackly: describes fractures that have rough edges. Uneven or irregular: minerals that break into rough,

uneven surfaces.

hardness

A mineral's hardness is a measure of its relative resistance to scratching, measured by scratching the mineral against another substance of known hardness on the Mohs Hardness Scale. This method is especially useful for identifying minerals in the field because you can test minerals against some very common objects (fingernail, a penny, a nail).

Sketch this chart into your field guide

Crystal structure

The unique arrangement of atoms in a crystal. A crystal structure is composed of a set of atoms arranged in a particular way; which is periodically repeated in three dimensions on a lattice.

Color streak

Mineral streak is the colored powder that a mineral leaves behind when it is crushed or dragged on a rough surface.

Test: rub the edge of a mineral against an unglazed porcelain tile (streak plate).

Minerals with a hardness less than 7 will leave a streak. Many mineral streaks will be white, so always look carefully.

Minerals harder than 7 will not leave a streak and might even scratch the streak plate itself.

Special properties

Many minerals have unique properties, such as radioactivity, fluorescence under black light, or reaction to acid. In most cases, it is necessary to observe a few properties to identify a mineral. Special properties can help to make the identification process easier, and more accurate.

• Malleability (easy to shape)

• Odor• Soapy feeling• Greasy feeling• double refraction

• Fluorescence (glow under UV light)

• Magnetic• Radioactive• Effervescent (Fizzes-gives off CO2)

in acid

Special properties

Mineral groups

Silicates: minerals that contain silicon and oxygen, and usually one or more other elements; 96% of minerals found in Earth’s crust EX: feldspar and quartz (most common minerals); unique structure accounts for the diversity of silicates.

Carbonates: minerals composed of one or more metallic elements with the carbonate compound. EX: calcite, dolomite, and rhodochrosite; primary minerals found in rocks such as limestoneand marble; distinct colorations.

Oxides: compounds of oxygen and a metal; hematite and magnetite are iron oxides (good source of iron); EX: uraninite valuable for source of uranium (generates nuclear power).

Halides: Minerals formed by combining a metal with one of the five halogen elements, chlorine, bromine, fluorine, iodine, and astatine. Many of these compounds will dissolve in water, and have low hardness. EX: Calcite

Sulfides: minerals that contain sulfur and one or more metals or semimetals. EX: Pyrite is a sulfide made from iron and sulfur.

Native Elements: minerals with a molecular structure of only one element. EX: are Copper, Sulfur, and Diamond.