Introduction to rock types and basic descriptions Flashcards
What titles will go on the rock hand specimen description?
Specimen number
Location
Colour
relative density
Strength
Texture: Crystal/ grain size
Crystal texture
Fabric
Other features
Sketches
What are the 3 quantitative expressions of colour?
Hue
Chroma
Value
What is hue when describing colour?
basic colour or mixture of colours
What is chroma when describing colour?
brilliance or intensity of colour
What is value when describing colour?
lightness of colour
What are some examples of hue being used to describe colour?
Light
Dark
What are some examples of chroma being used to describe colour?
Pinkish
Reddish
Yellowish
Brownish
Orangish
Greenish
Bluish
Purplish
Greyish
What are some examples of value being used to describe colour?
Pink
Red
Yellow
Orange
Brown
Green
Blue
Purple
White
Grey
Black
What are the 2 broad classifications for colour distribution?
Uniform- all one
Non-uniform
What are the general types of non-uniform colour distribution?
Spotted
Mottled
Dappled
Streaked
Striped
What are the 3 subdivisions for rock density?
High
Medium
Low
(for a rock of their size)
What is rock texture?
refers to the general physical appearance of a rock
What is the description of texture like for Igneous and metamorphic rocks?
Fine-grained < 0.75 mm
Medium grained 0.75-1 mm
Coarse-grained 1-2 mm
Very coarse-grained > 2 mm
What are Equigranular metamorphic or igneous rocks? (crystal/ grain relationship)
crystals or grains of the same size or approximately the same size
What are Inequigranular metamorphic or igneous rocks? (crystal/ grain relationship)
characterised by a mixture of crystals or grains of significantly different sizes.
What are Megacrystic metamorphic and igneous rocks? (crystal/ grain relationship)
containing crystals or grains that are significantly larger than the surrounding
groundmass or matrix
What are Aphanitic metamorphic or igneous rocks? (crystal/ grain relationship)
he individual constituents (e.g. crystals) are not visible to the naked eye.
What are porphyritic metamorphic or igneous rocks? (crystal/ grain relationship)
igneous rock containing large crystals (phenocrysts) that are compatible in
composition and mode of formation with the groundmass or matrix in which they occur (special
type of megacrystic texture)
What are crystalline metamorphic or igneous rocks? (crystal/ grain relationship)
consisting of clearly recognisable crystals using a hand lens or normal petrological
microscope
What are Cryptocrystalline metamorphic or igneous rocks? (crystal/ grain relationship)
rock consisting of crystals that are too small to be recognized and
distinguished separately under an ordinary microscope
What is fabric when describing rocks?
refers to the arrangement of the constituent grains or crystals in a rock
What are the 3 underlying processes which generate the planar features of rock ? (Fabric)
Layering
Lamination
Foliation
What is layering? (rock fabric)
alternating layers of crystals with subtle to clear differences
in mineralogy, often visible as some degree of colour banding
What type of rock is layering most common in?
Igneous
What type of rock is foliation typical of?
metamorphic rocks
What is foliation? (rock fabric)
layered or banded appearance, normally with distinct mineral compositions
What is the reason the layering occurs in igneous rocks?
Related to crystal settling and fluctuating melt composition in cooling magmas
What is the reason foliation occurring in metamorphic rock?
produced by exposure to heat under a directed pressure field
What type of of rock does laminations typically occur in?
sedimentary rocks
What is laminations? (rock fabric)
layering caused by small differences in the type of sediment including grain size, clay percentage, organic material content or mineral content
