1. 2.3 – Physical Properties of Minerals
Each mineral has specific properties that are the result of its chemical composition and crystalline structure.
These properties provide useful clues for identifying minerals.
Many of these properties can be identified by simply looking at a sample of the mineral or through simple tests.

2. Color color: what color the surface appears
property is easily observed but is VERY unreliable because minerals can be affected by impurities or weathering

3. Streak streak: color of a mineral in powdered form
more reliable than color for identification
rub the mineral against an unglazed tile called a streak plate

4. Luster luster: way a mineral reflects light
metallic: reflects light like a polished metal

5. nonmetallic: doesn’t reflect light like a metal
glassy
pearly
earthy (dull)

6. Cleavage & Fracture
cleavage: mineral breaks along planes of weakness to form smooth, flat surfaces

7. fracture: mineral breaks along irregular, rough surfaces (not flat!)
conchoidal: breaks in a circular pattern (like chipped glass)

8. Hardness hardness: ability of a mineral to resist scratching
Mohs hardness scale: scale against which the hardness of minerals is rated
1 = softest
10 = hardest
strength of the bonds that make up a mineral’s structure determines the hardness of that mineral

10. to calculate hardness
fingernail: penny: glass plate: 5.5
try to scratch mineral with fingernail – if it can then the hardness is “less than 2.5”; if not, try with penny
if penny scratches mineral, hardness is “2.5 – 3.5”; if not, try the glass plate
try to scratch the glass with the mineral – if it can’t then the hardness is “3.5 – 5.5”; if it can then the hardness is “greater than 5.5”

11. Crystal Shape
crystal shape: general shape of mineral due to atoms always combining in the same pattern

12. Density (Specific Gravity)
density: ratio of mass to volume in a substance
density = mass  volume
density remains the same regardless of size or shape of mineral
if you cut a mineral in half, you would have half the mass and half the volume so the same density (ratio!)

13. Special Properties of Minerals
Fluorescence & Phosphorescence
fluorescence: ability to glow under ultraviolet light
phosphorescence: ability to glow after the ultraviolet light is turned off

14. Chatoyancy and Asterism
chatoyancy (cat’s-eye effect): mineral displays a silky appearance in reflected light
asterism: a six-sided star appears when a mineral reflects light

15. Double Refraction
double refraction: produce a double image of any object viewed through the mineral

16. Magnetism Radioactivity
magnetism: minerals attracted to magnets
these minerals may be magnetic themselves
nonsilicate minerals that contain iron are more likely to be magnetic than silicate minerals
Radioactivity
radioactivity: unstable atoms (isotopes!) decay by releasing particles & energy to form stable atoms