Minerals and their characteristics

Physical Properties of Minerals Color: the color a mineral appears to the eye, under white or natural light. –Not effective in identifying few minerals because … Some minerals are similar in color. Some come in multiple colors. Others can have their color changed.

Physical Properties of Minerals LUSTER: the way a mineral reflects light. –Metallic Luster: shining like polished metal. (Ex: Pyrite, Galena, Hematite, Magnetite) –Non-metallic Luster: shining like polished glass, silk, wax, or any other shiny non-metal. (Ex: Diamond, Quartz, Opal.) –There is great variation between metallic and nonmetallic luster. –A mineral that does not reflect light is said to have an “earthy” luster.

Other acceptable adjectives for luster: –A–Adamantine (most lustrous, like diamond) –V–Vitreous (glassy) –D–Dull (little or very little shine at all) –G–Greasy (oily, slick-looking) –W–Waxy (like the shine off of a candle) –R–Resinous (like tree sap) –P–Pearlescent (like a … pearl) –A–Adventurine (glittery) These terms are often combined (viterous greasy) Physical Properties of Minerals

Streak: the color of the powder a mineral leaves after rubbing it on a “streak plate”. –More effective than color because the color of the streak is often different from the color of the mineral. –The streak can be more distinct to the mineral than the color.

Physical Properties of Minerals Hardness: a mineral’s resistance to being scratched. Moh’s Hardness Scale: The hardness of minerals relative to each other/scratching implements. –The scale is from 1-10, with 1 being the softest and 10 being the hardest.

Physical Properties of Minerals Moh’s Scale MineralTools 1Talc Fingernail (2.5) 2Gypsum 3Calcite Steel Nail (4.5) (Avoid the point) 4Fluorite 5Apatite Glass (5.5) 6Feldspar 7Quartz Streak Plate (5-8) 8Topaz 9Corundum 10Diamond

Physical Properties of Minerals Cleavage the tendency of a mineral to split along a certain plane or planes. not all minerals have cleavage. described in numbers of planes and angles of intersection.

Physical Properties of Minerals Fracture when minerals don’t break along typical cleavage planes. all minerals exhibit fracture. EXAMPLES: Conchoidal: shell-like and smooth Hackly: rough, jagged edges Fibrous: breaks into strands

Other types of fracture: –Uneven –Earthy –Even (smooth) Physical Properties of Minerals Novaculite Novaculite was used by native American Indians (especially in the southeast) to make arrowheads and other tools. The fracture and cleavage of this mineral is key to its usefulness.

Special Properties of Minerals These are properties that are not present in all minerals, but are extremely useful in ID’ing the minerals that have them Texture: Having a unique feel to the touch (talc, graphite) Effervesces: Reacts by bubbling when exposed to acid (calcite, dolomite) Taste: What does it taste like?… Duh… (Halite/Rock Salt)

Special Properties of Minerals Smell: What do you think the definition is? (Sulfur smells like eggs) Magnetic: Why would I write anything here? (Magnetite) Density: Basically the amount of water it displaces. (Crystals with a metallic luster are generally denser.) Phosphorescence: Does it glow under black light? (Fluorite)