4 Minerals Flashcards
Radioactivity
minerals which contain radioactive elements, such as radium, uranium, and thorium, as they are unstable they emit radiation as they breakdown into daughter elements.
-A spectrometer can detect gamma rays emitted during radioactive decay.
Fluorescence
-some minerals emit light when exposed to ultra violet radiation, this property is called fluorescence.
-the fluorescence colour is determined by the minerals physical and chemical structure
Magnetism
-Minerals attracted to magnets
-minerals that are magnetic usually contain iron
Twinning
The change in the direction of growth within a crystal.
-crystals that grow through each other are incentivised as penetration twinning and commonly seen in the mineral fluorite
Density and specific gravity
The mass or quantity of a substance per unit volume expressed in cubic centimetre or grams.
S.G = weight in air
———————-
weight in air — weight in water
Habit
Describes the shapes minerals tend to form. Growth rate of crystals, particularly the rate of crystallisation and amount of space around in the crystal affect, the final habit of the mineral.
Shapes of single, Crystal habits include acicular, columnar, equant, bladed, tabular, pisolitic, prismatic, foliated, fibrous, radiating,
Shapes of aggregate Crystal habit include concretionary, botryoidal, mammillary, stalactitic, dendritic, massive.
Fracture
-Fracture is when a mineral breaks or chips to form irregular surfaces. The nature of the surfaces describes the type of fracture.
-Conchoidal fracture is nice and smooth. Hackly fracture is very irregular. Uneven fracture is in the middle.
Cleavage
The tendency of a mineral to break along smooth, flat parallel planes of weakness within crystalline lattice
Described by direction it breaks (e.g. Mica breaks in one directional planes called basal. spodumene splits into directions known as prismatic. Calcite breaks in three directions, known as cubic.)
Hardness
-Hardness in minerals can be defined as a minerals resistance to scratching by other minerals.
-In every case the harder mineral scratches the softer mineral.
On the hardness scale ,
1. talc (pencil lead)
2. gypsum (fingernail)
3. calcite
4. fluorite (copper coin or wire)
5. apatite
6. orthoclase feldspar (pen knife blade)
7. quarts (steel file)
8. Topaz
9. sapphire/ruby (tungsten carbide)
10. diamond
What are the physical properties of minerals?
Physical properties of minerals include colour, streak, lustre, transparency, hardness, cleavage, fracture, habit, density, and specific gravity, twinning, magnetism, fluorescence and radioactivity.
What is a mineral?
Minerals are inorganic, naturally occurring crystalline solids with fixed or limited compositions. Atoms within minerals are crystalline, meaning they have a regular atom arrangement which is three-dimensional.
Colour
-Colour is determined by which wavelength of light are absorbed by the object and which are reflected.
-colour can be due to their mineral composition. -Colour can change when exposed to heat, light or electromagnetic radiation.
Colour isn’t a primary diagnostic mineral property as there maybe many variations in a single mineral type (e.g. pink or white diamonds)
Streak
streak is the colour of the powdered form of the mineral. To mark a mineral, the tile it’s marked on must be harder than the mineral itself.
Lustre
The appearance of light on the surface of a mineral. Described in quality and intensity. Descriptive terms that describe general appearance include metallic waxy and pearly. Descriptive term that describe intensity are dull or bright.
Descriptive words include metallic, submetallic, adamantite, pearly, resinous, waxy, specular, dull, vicious, silky.
Diagnostic property
Transparency
The ability of a mineral to transmit light
The term double refraction is used to describe a phenomenon that produces a duplication of an object, because the reflection of light at different speeds along different pathways, through the crystalline lattice of the rock.
