ROCKS & MINERALS Topic 10 quartz

What is a mineral? a naturally occurring, inorganic, crystalline solid with a definite chemical composition.

Definition of a mineral has 5 parts…

1. naturally occurring formed in nature and is not made by man. Ex) concrete and glass are not minerals.

2. Inorganic it has not been made by or composed of life forms. Fossil fuels and pearl are not minerals.

3. Crystalline its atoms have a specific arrangement (crystal structure).

CRYSTAL STRUCTURE The pattern or internal arrangement of atoms that characterizes each mineral; also called atomic structure.

4. solid

5. definite chemical composition. the types and ratio of elements that make up the mineral remains constant. Ex) NaCl rock salt one sodium atom for each chlorine atom

MINERAL COMPOSITON OF THE EARTH’S CRUST see ESRT – pg 1 & 16 (first and last page) - pg 6 & 7 – minerals named in types of rocks

99% of the Earth’s crust is composed of 8 elements. Two most common elements by mass are… oxygen silicon Two most common elements by volume are… potassium

Silica Tetrahedron Minerals that contain oxygen and silicon are called silicates.

Silicates make up approximately 90 % of the minerals in Earth’s crust.

The basic building block for silicates is the silica tetrahedron.

A tetrahedron is a pyramid composed of four equilateral triangles.

The silica tetrahedron (SiO4) is composed of a central silicon atom surrounded by 4 oxygen atoms.

Individual silica tetrahedron can combine in a number of different ways, producing many different types of minerals.

PROPERTIES OF MINERALS

Physical properties of a mineral are determined by either…. 1 - chemical composition. color luster streak 2 - crystal structure (arrangement of atoms) hardness cleavage crystal form

PROPERTIES CAUSED BY CHEMICAL COMPOSITION

1- COLOR Color is not useful when identifying a mineral. There are three reasons why…..

1) Many different minerals have similar colors.

2) One mineral may occur in different colors. Pure quartz is colorless or white. A small amount of iron give quartz a purple color. A small amount of titanium results in pink quartz.

3) Some minerals change color when exposed to air. In air, the brass-yellow color of chalcopyrite tarnished to bronze.

2 - LUSTER the way a mineral looks or shines in reflected light.

There are two (major) types of luster. 1) Metallic shines like polished metal. 2) Non-metallic does not shine like polished metal.

3 - STREAK Streak is the color of the powder of a mineral. Streak is determined by rubbing the mineral on a streak plate.

The streak of a metallic mineral is…... dark and distinct. The streak of a nonmetallic mineral is colorless or white. Streak is not very useful for nonmetallic minerals.

PROPERTIES (chemical & physical) CAUSED BY CRYSTAL STRUCTURE (determined by the internal arrangement of atoms)

CARBON BONDING HARDNESS CLEAVAGE MINERAL NAME 1-2 10 1 4 graphite diamond

1 - HARDNESS Hardness is the resistance of a mineral to being scratched. usually measured by using Mohs hardness scale.

“Mohs’ scale?” measures the hardness of any common material. scale goes from 1 to 10. The hardest mineral (10) is… Diamond The softest mineral (1) is… Talc

m < 2.5 2.5 – 5.5 m > 5.5 2.5 5.5 1 10 Hardness Scale if fingernail scratches… if it scratches glass plate m < 2.5 2.5 – 5.5 m > 5.5 2.5 5.5 1 fingernail glass plate 10 Hardness Scale

2 - CLEAVAGE When a mineral breaks, smooth to semi-smooth parallel surfaces are produced.

FRACTURE the way in which a mineral breaks producing an uneven breaking surface.

3 - CRYSTAL SHAPE (form) Crystal shape is the outward shape of a mineral specimen. also called crystal form. it reflects the internal atomic structure

Special Properties

1) Acid Test Calcite will react with hydrochloric acid. a drop of acid will fizz. the acid will dissolve the calcite.

2) magnetic a magnet will be attracted to the mineral.

3) taste halite has a salty taste.

4) fluorescence these minerals will glow while under ultraviolet light.

5) radioactive these minerals give off subatomic particles that will activate a Geiger counter.

6) double refraction this causes two images to be seen when the object is viewed through the mineral specimen.

The two most abundant elements by mass in Earth’s crust are oxygen and (1) potassium (3) nitrogen (2) hydrogen (4) silicon

2) The internal atomic structure of a mineral most likely determines the mineral’s (1) color, streak, and age (2) origin, exposure, and fracture (3) size, location, and luster (4) hardness, cleavage, and crystal shape

Base your answers to questions 3 and 4 on the diagram below, which shows three minerals with three different physical tests, A, B, and C, being performed on them. 3) Which sequence correctly matches each test, A, B, and C, with the mineral property tested? A—cleavage; B—streak; C—hardness (2) A—cleavage; B—hardness; C—streak (3) A—streak; B—cleavage; (4) A—streak; B—hardness; C—cleavage

Base your answers to questions 3 and 4 on the diagram below, which shows three minerals with three different physical tests, A, B, and C, being performed on them. 4) The results of all three physical tests shown are most useful for determining the rate of weathering of the minerals (2) identity of the minerals (3) environment where the minerals formed (4) geologic period when the

5) A human fingernail has a hardness of approximately 2. 5 5) A human fingernail has a hardness of approximately 2.5. Which two minerals are softer than a human fingernail? calcite and halite (2) graphite and talc (3) sulfur and fluorite (4) pyrite and magnetite

6) An unidentified mineral that is softer than calcite exhibits a metallic luster and cubic cleavage. This mineral most likely is (1) galena (3) halite (2) pyrite (4) pyroxene