Chapter 30 Minerals and Their Formation

Background Rocks are made up of minerals like how atoms make up molecules Rocks are made up of minerals like how atoms make up molecules Most minerals are compounds of different elements Most minerals are compounds of different elements Most minerals are not perfect like we will see in class…they are just blobs in rocks because of where they are formed Most minerals are not perfect like we will see in class…they are just blobs in rocks because of where they are formed

Physical Properties of Minerals (KNOW!) Mineral appearance Mineral appearance Mineral appearance Mineral appearance Crystal form and color Crystal form and color Hardness Hardness Hardness Luster Luster Luster Specific gravity Specific gravity Specific gravity Specific gravity Streak Streak Streak Cleavage and fracture Cleavage and fracture Cleavage and fracture Cleavage and fracture

Crystal Form Crystal Form: orderly arrangement of atoms in a crystal (what a crystal looks like is its arrangement) Crystal Form: orderly arrangement of atoms in a crystal (what a crystal looks like is its arrangement) Example: Quartz = six-sided prisms and asbestos = narrow fibers Example: Quartz = six-sided prisms and asbestos = narrow fibers When two or more minerals contain the same elements in the same amounts but they are arranged different it is a POLYMORPH When two or more minerals contain the same elements in the same amounts but they are arranged different it is a POLYMORPH Ex. Graphite and diamond Ex. Graphite and diamond

Quick Question We can identify minerals by their physical characteristics but why is it hard to identify minerals solely by their crystal form? We can identify minerals by their physical characteristics but why is it hard to identify minerals solely by their crystal form?

Hardness A measure of how easily a mineral can be scratched or how resistant it it to being scratched A measure of how easily a mineral can be scratched or how resistant it it to being scratched Ex. Diamond can scratch glass Ex. Diamond can scratch glass

Hardness Cont. Why is a diamond so much harder than another mineral? Why is a diamond so much harder than another mineral? The bonds that hold the atoms together are basis for the minerals strength. The bonds that hold the atoms together are basis for the minerals strength. Gold has larger atoms and is loosely packed so it has weaker bonds (24K gold is VERY soft) Gold has larger atoms and is loosely packed so it has weaker bonds (24K gold is VERY soft) Diamonds are made of little carbon atoms so it is tightly packed (a diamond is very hard) Diamonds are made of little carbon atoms so it is tightly packed (a diamond is very hard)

Another look Mohs Hardness Scale Mineral Talc Gypsum Calcite Fluorite Apatite Feldspar Quartz Topaz Corundum Diamond Rating 1Softest known mineral. It flakes easily when scratched by a fingernail. 2A fingernail can easily scratch it. 3A fingernail cannot scratch it, but a copper penny can. 4A steel knife can easily scratch it. 5A steel knife can scratch it. 6Cannot be scratched by a steel knife, but it can scratch window glass. 7Can scratch steel and hard glass easily. 8Can scratch quartz. 9Can scratch topaz. 10Hardest known mineral. Diamond can scratch all other substances. Testing Method

Cleavage Cleavage is the way that mineral breaks, its planes of weakness. Cleavage is the way that mineral breaks, its planes of weakness. Minerals that break along smooth, flat surfaces have cleavage. Minerals that break along smooth, flat surfaces have cleavage. Ex. Mica has cleavage Ex. Mica has cleavage

and Fracture!... Mineral that breaks uneven, rough, or jagged surfaces have fracture. Mineral that breaks uneven, rough, or jagged surfaces have fracture. Quartz has fracture Quartz has fracture quartz

Luster The way a mineral reflects a light luster. The way a mineral reflects a light luster. Does not depend on color! Does not depend on color! Either metallic or nonmetallic Either metallic or nonmetallic

Streak While colors helps us identify minerals it isn’t super reliable While colors helps us identify minerals it isn’t super reliable When a mineral is rubbed across a piece of porcelain tile a streak of powdered mineral is left behind. When a mineral is rubbed across a piece of porcelain tile a streak of powdered mineral is left behind. Streak: color given off in its powered form (important for minerals with a metallic or semi- metallic luster Streak: color given off in its powered form (important for minerals with a metallic or semi- metallic luster

Specific Gravity The specific gravity of a mineral is the ratio of its weight compared with the weight of an equal volume of water. The specific gravity of a mineral is the ratio of its weight compared with the weight of an equal volume of water. Gold has specific gravity of 19 Gold has specific gravity of 19 It means gold is 19 times heavier than water. It means gold is 19 times heavier than water. 19 times heavier

Quick Question Why is panning for gold possible? Why is panning for gold possible?

Chemical Properties Taste test and Acid Test Taste test and Acid Test Taste test helps identify salts Taste test helps identify salts Never taste minerals without being an expert some minerals are actually poisonous Never taste minerals without being an expert some minerals are actually poisonous Some minerals react with acid and “fizz” Some minerals react with acid and “fizz” Carbonate minerals react Carbonate minerals react

30.2 Minerals into Rocks Minerals make up rocks and minerals are made of elements that are in the earth Minerals make up rocks and minerals are made of elements that are in the earth 1000’s of minerals and only about 24 common minerals 1000’s of minerals and only about 24 common minerals The 24 minerals are made up of mainly 8 elements (out of all 88 found on earth) The 24 minerals are made up of mainly 8 elements (out of all 88 found on earth) 8 elements are 98% of the crust 8 elements are 98% of the crust About ½ or 50% of the crust is oxygen About ½ or 50% of the crust is oxygen

5 groups of rock-forming minerals Silicates Silicates 90% of earths crust (oxygen and silicon bond to make quartz) 90% of earths crust (oxygen and silicon bond to make quartz) Oxides Oxides Oxygen with one or more metals (great economic importance) Oxygen with one or more metals (great economic importance)

5 groups cont. Carbonates Limestone, carbon and oxygen bonded Sulfides and Sulfates Sulfur as main element combined with metallic elements Fools gold

30.3 On the Way to Rocks Minerals are formed by crystallization Minerals are formed by crystallization Growth of a solid from atoms that form together in a certain arrangement Growth of a solid from atoms that form together in a certain arrangement Overall minerals are formed from the crystallization of magma and from the precipitation or evaporation of water Overall minerals are formed from the crystallization of magma and from the precipitation or evaporation of water

REVIEW SLIDES

An illustration appearance:luster,color and streak

An illustration cleavage and fracture