Physical Properties of Rocks and Minerals From: http://webmineral.com/data/Rhodochrosite.shtml

MINERALS MAKE UP ROCKS!

The Physical Properties of Minerals Color Streak Luster Hardness Cleavage Fracture Density/Specific Gravity Special Properties Color- color of mineral Streak- what color mark it leaves Luster- how much it shines Hardness- how hard it is Cleavage- How clean it cuts Fracture- How easy it breaks Density- how much matter is in a certain amount of space Special Properties- Unique things

Important Physical Properties II Color - Although an obvious feature, it is often unreliable to use to determine the type of mineral.

Hope Diamond: 44.5 carats http://www.nmnh.si.edu/minsci/hope.htm

Important Physical Properties III Streak - The color of a mineral in its powdered form; obtained by rubbing the mineral against an unglazed porcelain plate. Streak is usually less variable than color. Useful for distinguishing between minerals with metallic luster. Basically what color it leaves as you rub it

Important Physical Properties I Luster - This property describes the appearance of reflected light from the mineral's surface. Nonmetallic minerals are described using the following terms: vitreous, pearly, silky, resinous, and earthy.

Density and Specific Gravity Density - Defined as the mass divided by the volume and normally designated by the Greek letter, rho,  mass/volume; SI units: kg/m3 or kg m-3, but geologists often use g/cm3 as the unit of choice. Specific Gravity - Ratio of the mass of a substance to the mass of an equal volume of water. Note that water = 1 g cm-3. S.G. is unitless. Examples - quartz (SiO2) has a S.G. of 2.65 while galena (PbS) has a S.G. of 7.5 and gold (Au) has a S.G. of 19.3.

Crustal Minerals - 90% of what we see on the Earth’s surface

Important Physical Properties V Hardness - This is the resistance of the mineral to abrasion or scratching. This property doesn't vary greatly from sample to sample of the same mineral, and thus is highly diagnostic. It also is a direct reflection of the bonding type and internal atomic arrangement. A value is obtained by comparing the mineral to a standard scale devised by Moh, which is comprised of 10 minerals ranging in hardness from talc (softest) to diamond (hardest).

- Mohs’ hardness scale is the most commonly used hardness scale

Polymorphism and polymorphs Substances having the same chemical composition but different crystal structures. e.g. diamond and graphite Both minerals are composed of pure carbon, but diamond is the high pressure polymorph of graphite. This gives rise to extremely different physical properties. - The only reason that diamond is way harder than graphite is because of how different the bonding is

Polymorphism 3 mm Natural Octahedral Diamond Graphite & Calcite From: http://www.phy.mtu.edu/~jaszczak/diamond.html

Diamond vs. Graphite Crystal Structures - The bonding structure decides hardness Hardness: 10 Hardness: 1-2 From: http://www.molecules.org/elements.html#diamond

Fingernail Hardness (2.5) Scratches Gypsum (2)

Important Physical Properties VI Cleavage - Orientation and number of planes of weakness within a mineral. Directly reflects the orientation of weak bonds within the crystal structure. This feature is also highly diagnostic. Fracture - This describes how a mineral breaks if it is not along well defined planes. In minerals with low symmetry and highly interconnected atomic networks, irregular fracture is common.