Unit 3: Earth Materials Lesson 1: Identifying Minerals (Heath Earth Science pg )

Today’s Objectives Differentiate between rocks and minerals, including: Use physical and chemical properties to identify and classify selected rocks and minerals

Rocks and Minerals Mineral: a naturally occurring inorganic solid substance with a definite chemical composition and structure (pg. 34) Rock: a group of minerals bound together (pg. 63) So in other words, There are nearly 5000 known mineral species on earth Rocks are made of minerals

Identifying Minerals Using Their Physical Properties This concept of will be Broken down into 2 or 3 Lessons Today we will practice using 6 different properties associated with mineral identification Lab Activity – next day?

Identifying Minerals Identifying minerals are determined by composition and crystal structure. With this being said you don’t need to know the chemical composition or crystal structure to identify what mineral you have. The first objective is to first determine the set of properties that are characteristic of the mineral

The properties most often used to identify minerals are: Crystal form growth habit Cleavage Luster Color Hardness Specific Gravity Magnetism Streak Effervescence (HCl rxn) Fluorescence *We will look at the properties listed in red

Luster The quality and intensity of the light reflected from the mineral Two most important lusters are: Metallic Non-Metallic: Vitreous (glass) Resinous (resin) Pearly Greasy Silky Earthy Adamantine Waxy

Luster Silky Vitreous Greasy Pearly Resinous Waxy Metallic Earthy/Dull Adamantine

Color and Streak Color identification can be confusing and misleading therefore it is important to streak a specimen on a nonglazed porcelain plate, called a ‘streak-plate’ This provides a reliable color effect because there are no impurities that can skew the streak

Hardness Hardness is the relative resistance of a mineral to being scratched This is a distinctive property of minerals Governed by the crystal structure and by the strength of the bond holding the atoms together (the stronger the forces holding, the harder a mineral is) Talc (softest) Diamond (hardest) Mohs’ relative hardness scale (10 steps) Minerals higher on the hardness scale have the ability to scratch any mineral lower than itself

Moh's Hardness Scale HardnessMineralDescription 1TalcFingernail scratches it easily. 2GypsumFingernail scratches it. 3CalciteCopper penny scratches it. 4FluoriteSteel knife scratches it easily. 5ApatiteSteel knife scratches it. 6FeldsparSteel knife does not scratch it easily, but scratches glass. 7Quartz Hardest common mineral. It scratches steel and glass easily. 8TopazHarder than any common mineral. 9 Corundu m It scratches Topaz. 10DiamondIt is the hardest of all minerals.

Remember… IF the object scratch’s the surface of the mineral, the mineral has a hardness less than that of the object Mineral < Object IF the mineral scratch’s the surface of the object, the mineral has a hardness greater than the object Mineral > Object

Magnetism Place a magnet up to the mineral, if there is an attraction than the mineral is magnetic.

Effervescence Place a small amount of cold, weak Hydrochloric Acid on the mineral sample. If the sample bubbles white, then the mineral reacts to the HCl.

Talc: H 2 Mg 3 (SiO 3 ) 4 Colour- white, green, gray Hardness- 1 Streak- colorless Magnetism- no Luster- vitreous HCl- no

K-Feldspar: KAlSi 3 O 8 Colour- pink to white Hardness- 6 Streak- white/colorless Magnetism- no Luster- vitreous to pearly HCl- no

Hematite: Fe 2 O 3 Colour- reddish or silvery Hardness- 5-6 Streak- reddish Magnetism- no Luster- metallic or earthy HCl- no

Calcite: CaCO 3 Colour- varies Hardness- 3 Streak- white/colorless Magnetism- no Luster- non-metallic/waxy HCl- yes

Magnetite: Fe 3 O 4 Colour- black Hardness Streak- black Magnetism- yes Luster- metallic HCl- no

Pyrite: FeS 2 Colour- brass yellow Hardness- 6 – 6.5 Streak- greenish black Magnetism- no Luster- metallic HCl- no

Other Properties Here are a couple other properties used to identify minerals, but we will not be using them However, you should still understand HOW to use them

Crystal Form and Growth Habit Planer surfaces on ice intrigued Greek philosophers who applied the name ‘crystals’ to any body that grows with a planer surface Planer faces are characteristic of every mineral however the number and angle of faces separates them apart from each other. It is this angle that gives each mineral a distinctive crystal form (internal order)

Crystal Form and Growth Habit

Cleavage The tendency of a mineral to break in preferred directions along bright, reflective planer surfaces Broken fragments are bounded by cleavage surfaces that are smooth and planer Don’t confuse crystal faces with cleavage surfaces as cleavages are breakage surfaces whereas crystal faces are growth faces

Lab Activity Each student is to fill out their own Worksheet, but can work in partners 5 minutes to test the physical properties of each mineral sample After your time is up, I will let you know. Pass your mineral to the next group Remember to look at the number on the mineral you are testing and fill it in the corresponding sections HAVE FUN AND ASK QUESTIONS!!!