Mineral –a naturally occurring, inorganic, solid that has a crystal structure and a definite chemical composition

Crystal – a solid with particles that form a repeating patternStreak – color of the powder of a mineralLuster – how light reflects from a mineralCleavage – splitting easily along flat surfacesFracture – how mineral looks when broken apart in an irregular wayFluorescence – ability to glow under ultraviolet lightVein – narrow channel or slab of a mineral different from surrounding rockOre – rock that contains a metal or economically useful mineralSmelting – melting of an ore in order extract the metal or mineralAlloy – a mixture of two or more metalsGemstone – hard, colorful mineral with a brilliant or glassy luster

Minerals• more than 3,000 minerals identified• must occur naturally in crust• cannot come from something that was once alive• is always a solid, with a definite volume and shape• particles line up in a repeating pattern that is sometimes obvious and sometimes can only be seen under a microscope• has a definite chemical composition, almost all are

compounds• each has its own specific physical and chemical properties used to identify it

Identifying Minerals• hardness – use Mohs hardness scale which ranks 10 minerals from softest to hardest• color – easily observed but can be used for only a few minerals, many minerals occur in a variety of color• streak – observed by rubbing a mineral against a streak plate, streak will not vary among samples of same mineral• luster – another way to determine mineral as ones containing metal will be shiny• density – each mineral has a particular density• crystal structure – crystals grow atom by atom to form a

particular structure, classified into 6 groups based on number and angle of faces, called crystal systems

• cleavage – way mineral breaks apart, if splits easily along flat surface is said to have cleavage

• fracture – if breaks into irregular shape then is said to fracture• special properties – some glow under ultraviolet light, some

are magnetic, some radioactive, some react to acid, some have electrical properties

Mohs Hardness Scale

Formation of minerals• minerals used today formed several billion years ago• formed by crystallization of melted material or through

crystallization of material dissolved in water• size of crystal depends on rate of cooling, amount of gas in magma and chemical composition• if magma stays underground and cools slowly will develop large crystals• if magma close to surface and cools faster has no time for large crystals to form so will have small ones• if solution of mineral rich liquid flows into cracks and crevices in earth will form a vein • can have the solution evaporate which will leave thick deposits of mineral• many valuable minerals found in or near volcanic activity or mountain building area

Lab: Determining Hardness, Color, Streak, and Luster of a Mineral

Objective :

The purpose of this lab is to determine the hardness, streak, color and luster of various mineral specimens.

Materials:talc galena copper pennygypsum hematite glass plate or microscope slidecalcite pyrite steel nailfluorite biotite or streak platefeldspar muscovite magnifying glassquartz halite

Safety Precautions:Use lab aprons. Follow normal laboratory precautions.

Procedure:•Using your fingernail, the copper penny, glass plate and steel nail try to scratch each rock sample. Record your observations in Data Table 1.

Rock Samples Observations

Data Table 1

2.Complete Data Table 2 by scratching one mineral with another. If a mineral on Side A can be scratched by a mineral on Side B place a check in the correct space. If it cannot – leave it blank.

A - Mineral Being Scratched

Talc Gypsum Calcite Fluorite Feldspar Quartz

Talc

Gypsum

Calcite

Fluorite

Feldspar

Quartz

B Mineral Used to Scratch

Data Table 2

3. Now use Data Table 1 and Data Table 2 to determine where each sample will fall on Mohs Hardness scale. Place the samples on order from softest (1) to hardest (10) on Data Table 3.

Data Table 3

Mineral Hardness Number

4. Use a streak plate to determine the streak for each sample given. Place your findings in Data Table 4.

MineralColor of Mineral

Color of Streak

Data Table 4

5.Observe the luster of each sample and place your observations in Data Table 5.

Mineral Luster

Data Table 5

Conclusions:

1. Based on your findings which minerals were the four hardest?

2. Which samples would you recommend a person use for a counter or a floor in a kitchen that is being remodeled?

3. When given an unknown sample how would you go about determining what that sample is, using the tests from this lab?