What is a Mineral?

2. What is a Mineral? • A mineral is a: • Naturally occurring, • Inorganic, • Crystalline solid, • That has a definite chemical composition.

3. Some Minerals

4. What is a Rock? • A rock is a: • Naturally formed, • Consolidated material, • Composed of grains of one or more minerals.

5. Some Rocks

6. Mineral Characteristics • Minerals are classified based on their physical properties and chemical properties.

7. How Do We Identify Minerals? • We identify minerals using physical properties of: • Color and streak • Luster • Hardness • Cleavage • Fracture

10. Color and Streak • Color is the first thing that most people notice about minerals. • Color is a useful property but many minerals are found in a variety of colors. • Streak is the pulverized color of a mineral. • Streak is determined by scraping the sample across a porcelain plate.

12. Luster • Luster is the quality and intensity of the light that is reflected from the surface of a mineral. • Luster is described as metallic or non-metallic. • Non-metallic is more common, most importantly is glassy. • Earthy luster is uncommon but appears silky, or pearly.

13. Earthy and Metallic Luster

14. Hardness • Hardness is a minerals resistance to being scratched, or the “scratchability” of a mineral. • In order for a mineral to scratch another it must be harder. • Frederich Mohs made up a scale, called the Mohs Scale, to compare hardness.

16. Cleavage • Cleavage is the tendency of a mineral to break along one or more smooth, flat, lustrous surfaces. • Cleavage is described as perfect, good, or poor. • Different minerals have different planes of cleavage. • Examples: mica has one perfect plane, halite has three perfect planes

19. Fracture • Fracture is the way a mineral breaks other than cleaving. • Fracture is an irregular break pattern • Fracture can be described as uneven, conchoidal (shell-like), splintery, earthy (like clay)

21. Formation of Minerals All minerals are crystalline, ,made of atoms arranged in a pattern. Crystals are minerals with geometric shapes and smooth flat surfaces called faces. Each kind of mineral has its own crystal shape and will develop into this form if it has room to grow w/o restrictions.

22. Various Crystals

23. 6 Basic Crystal Systems • Cubic • Hexagonal • Orthorhombic • Monoclinic • Tetragonal • Triclinic

25. Chemical Composition • All minerals are made of elements and some minerals can be identified by their special chemical composition. • Some minerals are made up of only one element (such as gold, copper, sulfur). • Most minerals are made of compounds, two or more elements chemically combined.

26. Chemical Composition - Silicates • Silicates are the most common minerals and are combinations of silicon and oxygen with other elements. • Examples are quartz, feldspar, mica and hornblende.

27. Silicates

28. Chemical Composition - Carbonates • Carbonates are minerals which are compounds of 1 carbon atom and 3 oxygen atoms. • Examples are calcite and dolomite.

29. Calcite Carbonates Dolomite Calcite Color Varieties

30. Chemical Composition – Oxides and Sulfides • In an oxide, the mineral iron combines with oxygen. • Example is magnetite • In a sulfide, the mineral iron combines with sulfur. • Example is pyrite (fool’s gold)

31. Oxides and Sulfides Magnetite (Lodestone) and Pyrite (Fool’s Gold)

32. Structure of Minerals • Structure refers to the arrangement of the atoms in a mineral. • Silicon and oxygen, the most common elements in the Earth’s crust, combine chemically to form a structural unit in the shape of a tetrahedron (a four-sided solid triangle)