mineral identification basics
DESCRIPTION
Mineral Identification Basics. PHYSICAL PROPERTIES DIAPHANEITY. The manner in which minerals transmit light is called DIAPHANEITY and is expressed by these terms: (*). TRANSPARENT : A mineral is considered to be transparent if the outline of an object viewed through it is distinct. (*). - PowerPoint PPT PresentationTRANSCRIPT
Mineral Identification Basics• PHYSICAL PROPERTIES DIAPHANEITY
The manner in which minerals transmit light is called DIAPHANEITY and is expressed by these terms: (*)
TRANSPARENT: A mineral is considered to be transparent if the outline of an object viewed through it is distinct. (*)
TRANSLUCENT: A mineral is considered to be translucent if it transmits light but no objects can be seen through it. (*)
OPAQUE: A mineral is considered to be opaque if, even on its thinnest edges, no light is transmitted. (*)
Quartz with Spessartine Garnets
Mineral Identification Basics• PHYSICAL PROPERTIES DIAPHANEITY
TRANSPARENT: A mineral is considered to be transparent if the outline of an object viewed through it is distinct. (*)
Topaz from Topaz Mountain, Utah (*)
Mineral Identification Basics• PHYSICAL PROPERTIES DIAPHANEITY
Sylvite from Salton Sea, California (*)
TRANSLUCENT: A mineral is considered to be translucent if it transmits light but no objects can be seen through it. (*)
Backlit Apophyllite Crystals (*)
Mineral Identification Basics• PHYSICAL PROPERTIES DIAPHANEITY
Schorl - The black variety of Tourmaline (*)
OPAQUE: A mineral is considered to be opaque if, even on its thinnest edges, no light is transmitted. (*)
Mineral Identification Basics• PHYSICAL PROPERTIES CRYSTALS
A CRYSTAL is the outward form of the internal structure of the mineral.
The 6 basic crystal systems are: (*)
ISOMETRICHEXAGONAL
TETRAGONALORTHORHOMBIC
MONOCLINICTRICLINIC (*)Drusy Quartz on Barite
Mineral Identification Basics• PHYSICAL PROPERTIES CRYSTALS
ISOMETRIC - Fluorite Crystals
The first group is the ISOMETRIC. This literally means “equal measure” and refers to the equal size of the crystal axes. (*)
Mineral Identification Basics• ISOMETRIC CRYSTALS
ISOMETRICIn this crystal system there are 3 axes. Each has the same length as indicated by the same letter “a”.
They all meet at mutual 90o angles in the center of the crystal.
Crystals in this system are typically blocky or ball-like. (*)ISOMETRIC
Basic Cube
a3
a2
a1
Mineral Identification Basics• ISOMETRIC CRYSTALS
ISOMETRIC Crystal Model (*)
Within this ISOMETRIC crystal model is the OCTAHEDRAL crystal form (yellow) and the TETRAHEDRAL crystal form (shown by the black lines). (*)
Mineral Identification Basics• ISOMETRIC CRYSTALS
ISOMETRIC - Basic Cube (*)
a1
a3
a2
a3
a2
a1
Fluorite cube with crystal axes. (*)
Mineral Identification Basics• ISOMETRIC BASIC CRYSTAL SHAPES
Octahedron
Spinel
Cube
Fluorite Pyrite
Cube with Pyritohedron
Striations
TrapezohedronGarnetGarnet Garnet - Dodecahedron
These are all examples of ISOMETRIC Minerals.
(*)
Mineral Identification Basics• HEXAGONAL CRYSTALS
HEXAGONAL - Three horizontal axes meeting at angles of 120o and one perpendicular axis. (*)
a1
a2
a3
HEXAGONAL Crystal Axes
c
Mineral Identification Basics• HEXAGONAL CRYSTALS
HEXAGONAL Crystal Model (*)
HEXAGONAL
This model represents a hexagonal PRISM (the outside hexagon - six sided shape). The top and bottom faces are called PINACOIDS and are perpendicular to the vertical “c” axis.
Within this model is the SCALENOHEDRAL form. Each face is a scalenohedron. Calcite often crystallizes with this form. As the model rotates, the flash of light seen is from a scalenohedral face.(*)
Mineral Identification Basics• HEXAGONAL CRYSTALS
These hexagonal CALCITE crystals nicely show the six sided prisms as well as the basal pinacoid. (*)
(*)
Mineral Identification Basics• HEXAGONAL CRYSTALS
RHOMBOHEDRON
Dolomite
SCALENOHEDRON
Rhodochrosite
QuartzHanksite
Pyramid Pyramid FaceFace
Prism Prism FacesFaces
Prism Prism FacesFaces
Pyramid Pyramid FacesFaces
Vanadinite (*)
Mineral Identification Basics• TETRAGONAL CRYSTALS
TETRAGONAL
Two equal, horizontal, mutually perpendicular axes (a1, a2) (*)
TETRAGONAL Crystal Axes
a1a2
c
c
a2a1
This is an Alternative Crystal Axes (*)
Vertical axis (c) is perpendicular to the horizontal axes and is of a different length. (*)
Mineral Identification Basics• TETRAGONAL CRYSTALS
TETRAGONAL Crystal Model (*)
TETRAGONAL
This model shows a tetragonal PRISM enclosing a DIPYRAMID. (*)
Mineral Identification Basics• TETRAGONAL CRYSTALS
WULFENITE
Same crystal seen edge on.Same crystal seen edge on. (*)
Mineral Identification Basics• TETRAGONAL CRYSTALS
APOPHYLLITE (clear) on Stilbite (*)
This is the same Apophyllite crystal looking down the “c” axis.
The red square shows the position of the pinacoid (perpendicular to the “c” axis). (*)
C axis line
Mineral Identification Basics• ORTHORHOMBIC CRYSTALS
ORTHORHOMBIC
Three mutually perpendicular axes of different lengths. (*)
ORTHORHMOBIC Crystal Axes
ab
c
a
c
b
An Alternative Crystal Axes Orientation (*)
Mineral Identification Basics• ORTHORHOMBIC CRYSTALS
ORTHORHMOBIC Crystal Model (*)
ORTHORHOMBIC
This model shows the alternative axes where the vertical “c” axis is not the longest axis. (*)
The model shows the outside “brick” shape of the PRISM and the inner shape is a DIPYRAMID. The top and bottom faces are called PINACOIDS and are perpendicular to the “c” axis. (*)
Mineral Identification Basics• ORTHORHOMBIC CRYSTALS
Topaz from Topaz Mountain, Utah. (*)
Mineral Identification Basics• ORTHORHOMBIC CRYSTALS
The view above is looking down the “c” axis of the crystal. (*)
C axis
B axis
A axis
BARITE is also orthorhombic. (*)
C axis
A axis
B axis
(*)
Mineral Identification Basics• ORTHORHOMBIC CRYSTALS
STAUROLITE (*)
Prism View (*)
Pinacoid
View (*)
This is a Staurolite TWIN with garnets attached. (*)
Mineral Identification Basics• MONOCLINIC CRYSTALS
MONOCLINIC
In this crystal form the axes are of unequal length. (*)
MONOCLINIC Crystal Axes
a
b
c
But a and c make some oblique angle and with each other. (*)
Axes a and b are perpendicular. (*)
Axes b and c are perpendicular. (*)
Mineral Identification Basics• MONOCLINIC CRYSTALS
MONOCLINIC Crystal Model
MONOCLINIC
In this model the outside shape is the PRISM. It looks like a distorted brick - flattened out of shape.
Inside is the DIPYRAMID. (*)
Mineral Identification Basics• MONOCLINIC CRYSTALS
Gypsum Mica
Orthoclase
Top View (*)
Mineral Identification Basics• TRICLINIC CRYSTALS
TRICLINIC
In this system, all of the axes are of different lengths and none are perpendicular to any of the others. (*)
TRICLINIC Crystal Axes
a b
c
Mineral Identification Basics• TRICLINIC CRYSTALS
TRICLINIC Crystal Model (*)
TRICLINIC
Again in this model the outside shape is the PRISM.
Located within the prism is the DIPYRAMID. (*)
Mineral Identification Basics• TRICLINIC CRYSTALS
Microcline, variety Amazonite (*)
Mineral IdentificationMineral Identification RESOURCESRESOURCES
http://www.gc.maricopa.edu/earthsci/imagearchive/index.htm
For lots of useful images of minerals and more facts about minerals, check out this web site:
For lots of up-to-date information about the Museum’s activities, be sure and visit the Arizona Mining and Mineral Museum’s web site at:
http://www.admmr.state.az.us/musgen.htm
To contact the Arizona Department of Mines and Mineral Resources, the web site address is:
http://www.admmr.state.az.us/