Identifying minerals Ch 5 section 2

Bell ringer 10/29 What physical properties would you use to determine minerals?

Physical properties Color Streak Luster Cleavage/fracture Hardness Crystal shape density

Colored minerals

Color- Enough said……. Established based on chemical composition in our crystalline structure- idiochromatic minerals. Ions of certain elements are highly absorptive of selected wavelengths of light. chromophores; elements which possess strong pigmenting capabilities. and copper (Cu) are chromophores. Sulfur- yellows Cobalt- blue Copper- orange Chromium- deep reds/purples/ yellows Iron- red/orange/brown Manganese- deep reds and purples Not a reliable way (on it’s own) to identify minerals

streak Color of mineral in powdered form May use a streak plate (tile) to rub/scratch against May grind with hands May grind in a mortar and pestle More reliable way of identification Metallic- dark streak Nonmetallic- light streak

Streak- do all minerals leave a streak?

luster Shinyness Is light reflected? Metallic Nonmetallic If the mineral reflects light similarly to metals- polished look Nonmetallic Pearly, glassy, waxy, or brilliant shine to it

Cleavage vs. fracture Cleavage Fracture Mineral splits into neat ridges leaving a smooth plane(s) behind Splits occur at areas of weakness running parallel in the crystalline structure. Looks cut Not in even planes Break off into jagged pieces leaving a rough texture Uneven/irreagular fracture - sandpaper Fiberous fracture- splinters Conchoidal fracture- curved

Cleavage breaks

Cleavage breaks

Fracture breaks Uneven breaks Have curves or random pieces ( may feel gritty or dusty) Appears to be BROKEN

hardness Ability to resist scratches simple difficult Ability to resist scratches Resistance to breaking (cleavage and fracture) Resistance is due to its chemical structure and composition Mohs hardness scale Hardness is measured by the resistance which a smooth surface offers to abrasion. The degree of hardness is determined by observing the comparative ease or difficulty which one mineral is scratched by another.

shape Minerals typical can take the shape of 6 basic crystal forms Isometric/cubic Tetragonal Monoclinic Orthorhombic Hexagonal triclinic

Density- i.e. specific gravity Density (or Specific Gravity) is a very important property of minerals. D= mass/volume. It is measured using various apparatus and techniques which are covered in most mineralogy textbooks. These are: Jolly Balance Triple Beam Balance Pycnometer Heavy Liquids Of these methods, the jolly and triple beam balance methods are best suited for mineral specimen work. Simple/ easy to construct

Density- # atoms/ space d= m/V

Special properties What do the following have in common? Florescence Phosphorescence Chatoyancy Asterism Double refraction

Fluorescence- minerals change colors when exposed to UV rays Wavelengths reflected change due to some being absorbed causing a color change Phosphorescence- minerals continue to give off reflected wavelengths of different colors.

Special features Chatoyancy- “cat eye” Silky look Asterism- star shape appears with reflected light Double refraction- bending of light rays to produce a double image

Special properties Magnetism – attractive forces due to the combination of e- in the atoms of the mineral Contain iron (Fe) Radioactivity- instability of the p+ and n+- in the atom- energy is released