Rock-forming minerals make up the Earth’s crust…
What are the most abundant elements in the Earth’s crust (by mass)?
Oxygen (O) - 46% and Silicon (Si) - 28%
Composition of the Earth’s Crust Minerals are composed of elements and compounds, and are classified into TWO (2) main groups (based on chemical composition): 1.Silicates Contain silicon (Si) and oxygen (O) 96% of Earth’s crust 2.Nonsilicates Do not contain silicon
Crystal Structure The internal arrangement of atoms Determines: –Crystal form –Breaking pattern –Hardness
Diamonds and Graphite are both made of carbon What makes them look so different?
…the internal arrangement of atoms, and the bonds between them…
Diamond (a) vs. Graphite (b)
Do you know what we use graphite for?
How can we identify minerals? Based on their physical and chemical properties…
1. COLOR Why do you think color is not a good way to identify a mineral?
These 3 minerals are all samples of QUARTZ:
2. STREAK: the color of a mineral in POWDER form More reliable than color
3. LUSTER: the way a mineral’s surface reflects light
Two (2) Types of LUSTER: A. Metallic - looks like metal
B. Nonmetallic - does not look like metal Earthy (dull) Pearly Waxy Glassy
4. HARDNESS: the ability of a mineral to resist scratching
Mohs Hardness Scale: assigns a number from 1 to 10 10 is the hardest (diamond) 1 is the softest (talc) Estimate the hardness of a mineral by dragging the mineral on a piece of window glass to see if it scratches it: --if it does, its hardness is 5.5 or greater --if it does not, its hardness is less than 5.5
5. CLEAVAGE vs. FRACTURE: the way a mineral breaks CLEAVAGE: –splitting of a mineral along lines or flat surfaces –usually creates smooth surfaces and edges with the same angle
FRACTURE: –when a mineral breaks unevenly in a curved or irregular way
6. DENSITY (Specific Gravity) Each mineral has small range of possible densities. Good way to help identify minerals. M D V
Other Special Properties of Minerals… 1. MAGNETISM: minerals containing iron Magnetite
2. DOUBLE REFRACTION: bending of light to produce a double image of objects viewed through them Calcite
3. FLUORESCENCE – ability to glow under UV light 4. PHOSPHORESCENCE – ability to glow after the UV light is taken away
6. REACTION TO ACID Calcite with HCl (hydrochloric acid)