Mineral Identification LabPHYSICAL GEOLOGYDr. Gregg Wilkerson and Michael Oldershaw.1

Mineral Identification LabPurpose of Lab:to observe the various physical properties ofcommon rock forming mineralsto utilize the combination of physical properties anddetermine the proper identification and chemicalcomposition of common rock-forming mineralsto understand that minerals make up rocks.1

Mineral Identification LabWhat is a mineral?Mineral Definition (5 parts)Naturally occursHomogeneous solidInorganic (non-living)Definite chemical compositionDefinite crystalline internal structure2

Mineral Identification LabMineraloids (amorphous solid) Mineraloids are minerals that lack aninternal atomic structure. Mineraloids do not have melting points.Examples:What happens when one meltsglass?Try melting plastic3

Physical properties of MineralsMinerals are identified using physicalproperties. Mineral physical properties reflectthe chemical composition and crystallinestructure.Mineral Physical Properties:crystal formcolorcolor of powdered residuereflection of lightshape of the mineralhardnessspecial mineral properties4

Physical Properties – Mineral IDCrystal Form:Crystal form represents flat well-defined smoothcrystal faces that reflect the mineral’s internal atomicstructure.Observation:A mineral will show smooth flat surfacesor “crystal faces” that reflect a consistentangle between the faces for a particularmineral species.5

Various Crystal FormsAll quartz crystals, big, fat, skinny,will show consistent angles betweencrystal faces.6

Physical Properties – Mineral IDColorColor is the most noticeable physical propertybut the least accurate.The same mineral can occur in many differentcolors. Do not trust color.Observation:A mineral can be red, green, blue, white,clear, smokey and many other colors.7

Different color fluorite minerals8

Physical Properties – Mineral IDStreakStreak is the Color of the powdered residue left onthe porcelain streak plate.The mineral is scratched across the streak plate andthe color of the powdered residue is observed.Some minerals show different color powder than theactual color of the mineral.Observation:Observe the color of the powderedresidue left on the porcelain streak plate.9


LusterHow does the mineral reflect light. Is themineral metallic or non-metallic?Metallicresembles polished metalNon-metallicglossyvitreous (glassy)waxy, greasyearthy (concrete)resinousgreasypearlyObservation:Allow the light to reflect off the fresh mineral surface anddetermine if the mineral is metallic or non-metallic11

Incoming light wavesVery – Very smooth surfaceVery shinymineral surfaceIncoming light wavesSmooth surfaceshinymineral surfaceIncoming light wavesIrregular surfacedull lustermineral surface12

Cleavage Planes Cleavage represents the tendency of a mineral tobreak in preferred directions along bright,reflective plane surfaces. A mineral will break along atomic planes ofweakness, repeating the flat surfaces on smallerbroken pieces.Observation:Look for the cleavage planes by rotating themineral and observing “flashing of light” –like turning on/off a flashlight.13

Brakes along planes of weaknessFlashes of light (Checking for cleavage)Cleavage surfaces14


Fracture surfaces represent:non-planer, non-parallel surfaces that reflect light in anuneven “undulated” fashion. When broken, smallerpieces will not repeat themselves.Example: Once the crystal face is broken, the smoothflat surface will never again be observed.Observation:Observe cracks, fractures, destruction on the flat surfaceas well as non-repeating flat surfaces. Notice the randomor undulating reflective light as the mineral is rotated.16

Conchoidal fracture (dished shaped features)17

HardnessHow hard is the mineral – or how the mineralresists scratching.German mineralogist – Friedrich Moh (1773-1839)establishes moh’s scale of hardness.Observation:Does the mineral scratch glass?Yes – the mineral is hard 7No – mineral is 718

DiamondSoftestScale of hardnessnot evenly distributedTalcHardest19

Moh’s Scale of Hardness20

Special mineral properties:Reaction to Acid – Mineral will fizz when subjected to acid.Tenacity – Mineral will bend (elastic).Striations – Minerals display hairline grooves on crystal faces.Magnetism – Magnets are attracted to the mineral.Double refraction – An image beneath the mineral is repeatedor doubled.Specific gravity – How heavy is the mineral.Taste – Does the mineral have taste?21

Acid reaction(fizzing)StriationsDouble Refraction22

Mineral ID procedure:Use the process of elimination or narrowing down the mineralname.Luster – determine if the mineral is metallic or non-metallicHardness – Does the mineral scratch glass or not scratch glass?Cleavage planes – does the mineral show cleavage or fracture?Use charts – Use the mineral charts and narrow your field ofchoices to a select few. Carefully read the streakcharacteristics, color and any special physicalproperties – select the proper name and indicate thechemical composition.23

Mineral Identification Lab Purpose of Lab: to observe the various physical properties of common rock forming minerals to utilize the combination of physical properties and determine the proper identification and chemical composition of common rock-forming minerals to understand that minerals make up rocks. 1