Lab 3 Minerals

Objectives:

-Definition of a Mineral

-Properties of Minerals

-Identification of Minerals

-Rock Forming Minerals

What is a Mineral??

-all minerals are inorganic, naturally occurring substances that have a characteristic chemical composition, distinctive physical properties, and crystalline structure.

What about a Rock??

-simplest definition is just an aggregate of one, or many minerals.

-Mineral Properties-

Color

-Easiest to notice…BUT

-Many minerals come in different colors ie Quartz

-Colorless means clear, or transparent- like glass

-Colors come in different Clarities

*Transparent: clear, or see through

*Translucent: foggy, like frosted glass

*Opaque: no light gets through, like metal

Habit

-The way a crystal grows naturally, its characteristic “form”

ie… pyrite (fools gold) grows in cubes, so does galena. But quartz grows in prisms…etc

Luster

-Description of how a mineral reflects light

-All minerals have either Metallic, or Non-Metallic

*Metallic: Shiny like a metal – brass, silver, gold, steel etc

*Non-Metallic: May be reflective, but doesn’t look like metal- quartz, halite, biotite, muscovite etc

Note-metallic minerals tarnish and may need to be scraped to reveal a fresh surface

Streak

-Color of a mineral when powdered -ie scratched against ceramic

-hematite comes in many colors and lusters, but all have red streak

*Make sure the mineral you are streaking is not harder than the plate, or you will only be observing scratched off ceramic-not streak

Cleavage and Fracture

-Often confused w/ each other-

-Cleavage:

-when a mineral breaks along preferred directions dependent on its internal crystal structure

-Cleavage direction refers to planes within the crystal that line up with its preferred direction of breaking

-Cleavage has different qualities:

*Excellent- faces have perfectly flat surfaces

*Good- reflects light in spots, slightly uneven

*Poor- little reflected light, very uneven

*See Overhead Figure 3.12*

ex- galena

Fracture:

-When a mineral break cuts through crystals and “shatters” the mineral.

-If you smash a prism of qtz it doesn’t break into little prisms it shatters into a lot of fragments w/ no preferred shape- unlike galena…

*glass and qtz have special kind of fracture called Conchoidal Fracture. This looks like broken glass where you have arc shaped scoops. What else does this…think arrowheads

see figure 3.12 for a good summary…..

Hardness

-A measure of a minerals resistance to scratching.

ie- a harder mineral can scratch a softer one

BUT- we aren’t talking about breaking and being brittle…glass is a lot harder than talc, but you can easily throw a piece of talc through a glass window…

Look at Mohs Scale of Hardness Fig 3.9

Effervesce (rxn w/ acid)

-When you drip dilute HCl onto mineral it fizzes, that means it effercesces, good diagnostic for calcite- why?

Striations vs. Exsolution Lamellae

Striations- continuous parallel lines (look like scratches or steps) formed on crystal faces resulting from “twinning” of the crystals within the mineral…quartz has good striations

Exsolution Lamellae- discontinuous wormy intergrowths of one mineral within another. Forms often in feldspar minerals where you get a pink K-feldspar with little white wormy intergrowths of Na-feldspar-

Magnetism… its magnetic