Mineral physical properties

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Color:

Caused by the complex ways in which light interacts with the mineral’s composition and internal structure (almost never diagnostic)

Habit:

Refers to the shape in which a mineral often grows

luster

Refers to how light bounces off a FRESH mineral surface (how shiny it is)

Diaphaneity

How transparent or opaque a mineral is

Density

technically specific gravity, but for us just eyeballed how heavy it is vs how heavy it looks like it should be

Hardness

how easily a mineral’s surface is scratched

Tenacity

The mineral’s resistance to breaking.

Streak

the color of the trail of ground-up mineral bits if you scratch a mineral against a porcelain plate

Luminescence

A minerals “glow” caused from electrons jumping to a higher energy state when you shine a light on it

Flouresecne

A form of luminescence where the light you shine on it is UV.

Phosphoresence

A form of luminescence where the electron gets trapped in a higher energy state for a while, so the glow sticks around even after you take away the light source.

opalescence

minerals glinting different colors as the mineral is rotated

magnetism

minerals being magnetic

Effervescence

minerals fizzing when you drop HCL on them

taste

sometimes minerals have a certain taste!

Mohs hardness of talc

1

Mohs hardness of gypsum

2

Mohs hardness of calcite

3

Mohs hardness of fluorite

4

Mohs hardness of Apetite

5

Mohs hardness of orthoclase feldspar

6

Mohs hardness of quartz

7

Mohs hardness of topaz

8

Mohs hardness of corundum

9

Mohs hardness of diamond

10

Mohs hardness of pencil lead

1.5

Mohs hardness of fingernail

2.5

Mohs hardness of penny

3.5

Mohs hardness of pocket knife blade

5.5

glass

5.5

steel file

6.5

streak plate

7

Metallic luster:

Like polished metal

Sub-metallic luster:

looks like metal but not as shiny

Non-metalic luster:

Not shiny like metal

Vitreous luster:

like glass

Resinous luster:

looks like resin or glass (mostly amber colored minerals)

Greasy luster:

looks like it has grease on it

waxy luster:

looks like its surface is made of wax paper

silky luster:

like fine fibers

Adamantine luster

brilliantly shiny, like a diamond

Pearly luster

almost iridescent, like the inside of a seashell

Dull luster

Not at all shiny

Earthy luster

like dirt (leaves stuff on your hands!)

Blocky habit

Having square-ish cross-sections

Acicular habbit

Needle-like

Tabular habbit

Like thick sheets stacked together

Bladed

looks like a blade

Columnar/prismatic

Elongated in one direction

Micaceous

Easily split into sheets

Massive

Solid mass of crystals, without real form

dendritic

branching like a tree

Botryoidal

like a bunch of grapes

Drusy

Covered in fine crystals

4 main variables that contribute top a minerals color:

composition, impurities, structure, habit

Hematite color vs streak

usually black but red streak

Galena appearance (lookalike mineral) vs streak

looks like hematite but has a grey streak

Fluorite color vs streak

Usually blue or purple but has a white streak

Most silicate minerals have a what streak color?

white

3 types of fracture:

Uneven, chonchoidal, fiberous/spiny

4 concepts to describe cleavage:

Quality, direction, angle, habit

Basal cleavage habit:

1-direction, parallel to the mineral base.  Minerals look like they’re being peeled away, like biotite or muscovite

Cubic cleavage habit:

Mineral ends up looking like a cube, like galena. 

Octahedral cleavage habit:

Mineral ends up looking like two pyramids.  Pyramid-shaped wedges break off.  For example: fluorite.

Rhombohedral cleavage habit:

Mineral ends up looking like a rhombohedron (a tilted cube), e.g., calcite.

Indicators of a surface being a growth surface NOT a cleavage one:

Impurities (tiny pits or grooves in the surface), growth grooves / chatter marks, freshness of mineral surface (not fresh= might be a growth face)

Striations are:

extremely thin, long, parallel grooves cut into the surface of a mineral (often caused by twinning)

minerals in the Amphibole Group (Hornblende, Tremolite, Actinolite, Glaucophane, etc.) – all have what cleavage?

60˚/120˚

Minerals in the Pyroxene Group (enstatite, diopside, augite, etc.) – all have what cleavage?

approx. 90˚

Plagioclase will usually have what?

striations

Calcite and dolomite have what cleavage?

Rhombohedral

Quartz has what kind of fracture?

Conchoidal

Mica minerals have what kind of cleavage?

1-directional, perfect basal

The chrysotile form of serpentine by its has what kind of fracture?

Extremely fibrous