Mineral Identification Lab

PHYSICAL GEOLOGY

Dr. Gregg Wilkerson and Michael Oldershaw.

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Mineral Identification Lab

Purpose of Lab:

to observe the various physical properties of

common rock forming minerals

to utilize the combination of physical properties and

determine the proper identification and chemical

composition of common rock-forming minerals

to understand that minerals make up rocks.

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Mineral Identification Lab

What is a mineral???????

Mineral Definition (5 parts)

Naturally occurs

Homogeneous solid

Inorganic (non-living)

Definite chemical composition

Definite crystalline internal structure

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Mineral Identification Lab

Mineraloids (amorphous solid)

• Mineraloids are minerals that lack an

internal atomic structure.

• Mineraloids do not have melting points.

Examples:

What happens when one melts

glass?

Try melting plastic

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Physical properties of Minerals

Minerals are identified using physical

properties. Mineral physical properties reflect

the chemical composition and crystalline

structure.

Mineral Physical Properties:

crystal form

color

color of powdered residue

reflection of light

shape of the mineral

hardness

special mineral properties

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Physical Properties – Mineral ID

Crystal Form:

Crystal form represents flat well-defined smooth

crystal faces that reflect the mineral’s internal atomic

structure.

Observation:

A mineral will show smooth flat surfaces

or “crystal faces” that reflect a consistent

angle between the faces for a particular

mineral species.

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Various Crystal Forms

All quartz crystals, big, fat, skinny,

will show consistent angles between

crystal faces.

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Physical Properties – Mineral ID

Color

Color is the most noticeable physical property

but the least accurate.

The same mineral can occur in many different

colors. Do not trust color.

Observation:

A mineral can be red, green, blue, white,

clear, smokey and many other colors.

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Different color fluorite minerals

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Physical Properties – Mineral ID

Streak

Streak is the Color of the powdered residue left on

the porcelain streak plate.

The mineral is scratched across the streak plate and

the color of the powdered residue is observed.

Some minerals show different color powder than the

actual color of the mineral.

Observation:

Observe the color of the powdered

residue left on the porcelain streak plate. 9

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Luster

How does the mineral reflect light. Is the mineral metallic or non-metallic?

Metallic Non-metallic

resembles polished metal glossy

vitreous (glassy)

waxy, greasy

earthy (concrete)

resinous

greasy

pearly

Observation:

Allow the light to reflect off the fresh mineral surface and determine if the mineral is metallic or non-metallic

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Very – Very smooth surface

Smooth surface

Irregular surface

Very shiny

shiny

dull luster

Incoming light waves

Incoming light waves

Incoming light waves

mineral surface

mineral surface

mineral surface

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Cleavage Planes

• Cleavage represents the tendency of a mineral to

break in preferred directions along bright,

reflective plane surfaces.

• A mineral will break along atomic planes of

weakness, repeating the flat surfaces on smaller

broken pieces.

Observation:

Look for the cleavage planes by rotating the

mineral and observing “flashing of light” –

like turning on/off a flashlight.

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Brakes along planes of weakness

Cleavage surfaces

Flashes of light (Checking for cleavage)

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Fracture surfaces represent:

non-planer, non-parallel surfaces that reflect light in an

uneven “undulated” fashion. When broken, smaller

pieces will not repeat themselves.

Example: Once the crystal face is broken, the smooth

flat surface will never again be observed.

Observation:

Observe cracks, fractures, destruction on the flat surface

as well as non-repeating flat surfaces. Notice the random

or undulating reflective light as the mineral is rotated.

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Conchoidal fracture (dished shaped features)

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Hardness

How hard is the mineral – or how the mineral resists scratching.

German mineralogist – Friedrich Moh (1773-1839) establishes moh’s scale of hardness.

Observation:

Does the mineral scratch glass?

Yes – the mineral is hard > 7

No – mineral is < 7

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Scale of hardness

not evenly distributed

Talc

Diamond

Softest

Hardest19

Moh’s Scale of Hardness

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Special mineral properties:

Reaction to Acid – Mineral will fizz when subjected to acid.

Tenacity – Mineral will bend (elastic).

Striations – Minerals display hairline grooves on crystal faces.

Magnetism – Magnets are attracted to the mineral.

Double refraction – An image beneath the mineral is repeated

or doubled.

Specific gravity – How heavy is the mineral.

Taste – Does the mineral have taste??

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Acid reaction

(fizzing) Striations

Double Refraction

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Mineral ID procedure:

Use the process of elimination or narrowing down the mineral name.

Luster – determine if the mineral is metallic or non-metallic

Hardness – Does the mineral scratch glass or not scratch glass?

Cleavage planes – does the mineral show cleavage or fracture?

Use charts – Use the mineral charts and narrow your field of choices to a select few. Carefully read the streak characteristics, color and any special physical properties – select the proper name and indicate the chemical composition.

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