Download Rock Manual for Field Geology in Kumaun Region

Geology Manual
Properties of Minerals & Rocks
in the Kumaun Region
Compiled for CHIRAG
Prepared by:
Sophia Yee
B.Sc. Geology, M.Sc. Water Management
Montreal, Quebec, Canada
[email protected]
May 2013
SECTION 1: INTRODUCTION TO MINERALS & ROCKS
1.1 MINERALS
Minerals are composed of elements that are found in the periodic table. There are
numerous groups of minerals which are classified according to their chemical and physical
properties.
The main groups of minerals found in this region are as follows:
Table 1. The main groups of minerals in the Kumaun region
Mineral group
Name
Formula
SILICATES
Tectosilicates
Quartz
SiO2
(Feldspar Family)
Alkali Feldspar Orthoclase
KAlSi3O8
Plagioclase Feldspar Albite
NaAlSi3O8
Biotite
K(Mg,Fe)3(AlSi3)O10(OH)2
Muscovite
KAl2(AlSi3)O10(OH)2
Sericite
-
Talc/Soapstone
Mg3Si4O10(OH)2
Illite
(K,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2
H2O
Chlorite
(Mg,Fe)3(Si,Al)4O10(OH)2
(Mg,Fe)3(OH)6
Phyllosilicates/(Mica Group)
(Chlorite Group)
Inosilicates (Amphibole Group) Hornblende
(Ca.Na)23(Mg,Fe,Al)5Si6(Al,Si)2O22(OH)2
Carbonates/Evaporites
Calcite
CaCO3
Gypsum
CaSO4 2H2O
Limestone
CaCO3
Dolomite
(CaMg)(CO3)2
2
1.2 ROCKS
Rocks can be classified into three types: igneous, sedimentary and metamorphic. The simple
schematic below represents the rock cycle (see Figure 1).
Figure 1. A simplified representation of the rock cycle
Igneous rocks are formed either on the Earth’s surface (by the cooling of lava) or below the
surface with the crystallization of magma. Sedimentary rocks are formed by depositional
(transporting eroded particles) or evaporative processes in combination with “lithification”
(consolidating different layers of particles). Metamorphic rocks are formed under diagenetic
processes in which sedimentary rocks are buried and undergo changes in pressure and
temperature. Depending on the magnitude of these changes, a different rock can be born. The
specific classification of these rocks is done according to the graph of metamorphic facies
(see Figure 2).
Main facies:
Low T and low P = Zeolite
Moderate - high T and low
P = Prehnite-Pumpellyite
Low T - high P = Blueschist
Moderate - high T and
moderate P = Greenschist –
Amphibolite – Granulite
Moderate - high T and high
P = Eclogite
Figure 2. Metamorphic facies (see section 3 for a description of a metamorphic reaction)
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Table 2. Common rocks within (or outside of) the Kumaun region
Rock type
Name
Class
IGNEOUS
SEDIMENTARY
Basalt (w/ or w/o vesicles)
Extrusive/Volcanic
Granite
Intrusive/Plutonic
Conglomerate/Breccia
Clastic/fragmental
Sandstone
Clastic/fragmental
Mudstone/Claystone/Siltstone Clastic/fragmental
METAMORPHIC
Shale
Clastic/fragmental
Limestone
Organic/bioclastic
Dolostone
Crystalline
Slate
Low-grade
Phyllite
Schist
Medium-grade
Mica Schist
Green Schist
Talc Schist
Gneiss
High-grade
Augen Gneiss
Quartzite
Marble
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SECTION 2: PROPERTIES
2.1 MINERALS
Minerals have various chemical properties which are determined by their elemental
composition. However, only a domain of Geology, called mineralogy called “Spectroscopy”,
can be used to identify such microscopic features. For the purpose of field identification,
simple distinguishing features can be used:
1.
Color: not a diagnostic characteristic
2.
Hardness:
The “Mohs Scale of Hardness” (see Table 3) is used to determine the ‘relative’ hardness of a
mineral compare to the known hardness of a mineral or a standard object.
Table 3. The Mohs scale of Hardness
Hardness
Mineral
Formula
1
Talc
Mg3Si4O10(OH)2
2
Gypsum
CaSO4 2H2O
3
Calcite
CaCO3
4
Fluorite
CaF2
5
Apatite
Ca5 (PO4)3 (OH-, Cl-, F-)
6
Feldspar (Orthoclase)
KalSi3O8
7
Quartz
SiO2
8
Topaz
Al2 SiO4 (OH-, F-)2
9
Corundum
Al2O3
10
Diamond
C
Three common objects’ hardness value for comparative purposes:
Fingernail = 2.5
Coin = 3.0
Steel blade = 5.5
3.
Streak: the color a mineral gives off when rubbed against a surface (must be harder
than its own hardness.
4.
Cleavage: denotes the breaking pattern of a mineral along its regular surface
(depending on its crystal/chemical structure). This occurs when a mineral is strained beyond
its limits. A mineral that has cleavage surfaces (2 types: perfect or good) is contrasted to a
mineral that shows fracturing (i.e. breaking irregularly).
5.
Habit: the naturally occurring shape of a mineral (ex. Cubic, blocky, platy, etc).
2.2 INDIVIDUAL MINERAL PROPERTIES
A.
TECTOSILICATES – 3D framework, comprise 75% of the Earth’s crust
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QUARTZ
Formula: SiO2
Color: Colorless to milky whitegrey
H= 7
Streak= White
Concoidal fracture (breaks like
glass)
Habit: Crystalline(left) or
amorphous(right)
B.
FELDSPAR FAMILY
ORTHOCLASE
Formula: KAlSi3O8
Color: Reddish-pink
H= 6
Streak=White
One perfect, one good cleavage
Habit: Blocky, equant crystals
Micro (perthitic) veining is common
ALBITE
Formula: NaAlSi3O8
Color: Transparent to milky white
H=6-7
Streak=White
One perfect, one good cleavage
Often confused with Quartz, but
distinguished by uneven and blocky surfaces
C.
PHYLLOSILICATES
BIOTITE
Formula: K(Mg,Fe)3(AlSi3)O10(OH)2
Color: dark brown to blackish brown
H=2.5-3 (scratched by fingernail or coin)
Streak=grey
One perfect cleavage
Habit: lamellar with platy, flexible plates
Hexagonal outline of crystals
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MUSCOVITE
Formula: KAl2(AlSi3)O10(OH)2
Color: typically colorless, but thickness adds tint of
brown, yellow or pink
H=2.5-3 (scratched by fingernail or coin)
Streak= white
Luster: pearly, vitreous; transparent/translucent sheets
Perfect cleavage
Not resistant to chemical weathering and often
transformed to clay
Common in Schists and Gneisses
SERICITE
Formula:
Color: light brown
H=2.5-3 (scratched by fingernail or coin)
Streak=white
Luster: transparent/translucent sheets, but higher
luster and greasiness compared to Muscovite
Common hydrothermal alteration mineral
of Orthoclase and Plagioclase Feldspar
TALC / SOAPSTONE
Formula: Mg3Si4O10(OH)2
Color: grey-white, yellow-white
H=1 (scratched by fingernail)
Luster: pearly
Uneven fracture pattern
Habit: can have minor foliation or uniformly
indistinguishable crystals in masses
Formation: Caused by the weathering of Magnesium (Mg) due to heat and water
ILLITE
Formula: (K,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2 H2O
Color: white
H=1-2 (between Talc and Gypsum)
Habit: commonly found in aggregates
A K-deficient Muscovite, non-expanding and found
in masses
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CHLORITE
Formula:
(Mg,Fe)3(Si,Al)4O10(OH)2 (Mg,Fe)3(OH)6
Color: Black with a tint of green
H=2-2.5 (scratched by fingernail)
Streak= pale green to grey
Luster: vitreous
Perfect cleavage with lamellar fracturing
Habit= Usually found in aggregates/clusters of flakes
Classified between a mica and clay
D.
INOSILICATES/AMPHIBOLE GROUP
HORNBLENDE
Formula: (Ca.Na)2-3(Mg,Fe,Al)5Si6(Al,Si)2O22(OH)2
Color: Black to dark green
H=5-6 (scratched by steel blade)
Streak= pale grey
Luster: lustrous to dull
Imperfect cleavage and uneven fracture
E.
CARBONATES
CALCITE
Formula: CaCO3
Color: white
H=3 (scratched by coin)
Habit= rhombohedra; crystals present in clusters of
grains or small flakes
Reacts to HCl
EVAPORITES
GYPSUM / ROCK GYPSUM as sedimentary rock
Formula:
Color: white-grey
H=2 (scratched by fingernail)
Texture: greasy and fibrous
Luster: Translucent
One perfect cleavage, but typically massive
Note: For Limestone and Dolostone properties, see rock section
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2.3 ROCKS
Similar to minerals, rocks also have distinguishing features. Grain size is the most
important characteristic used for rock identification. In the case of igneous rocks, they are
classified as extrusive (volcanic) vs. intrusive (plutonic) rocks, which are differentiated by the
size of crystals present in the matrix (the finer-grained material that larger grains/crystals are
embedded within). For sedimentary rocks, they are classified as clastic/fragmental vs.
crystalline rocks, but grain size is only the feature used to differentiate between the former
category and the reaction to hydrochloric acid (HCl) determines the latter category.
A second important characteristic is the degree of deformation of a rock and it is used for
metamorphic rocks. There are low-, medium- and high-grade metamorphic rocks which have
an increasing degree of deformation, however, this isn’t a one-rule fits all and the mineral
assemblage is the ultimate judge for metamorphic rocks (as some minerals are restricted by
temperature (T) and pressure (P) conditions)).
2.4. INDIVIDUAL ROCK PROPERTIES
A.
IGNEOUS ROCKS
BASALT
CLASS: Extrusive (Volcanic)
Color: Black
Grain size: aphanitic (grains
not visible to naked eye) to
fine-grained
May contain few crystals
Can contain vesicles due to
the release of gas (picture on
right)
Formation: Low silica lava, formed at divergent plate boundaries (ex. Mid-oceanic ridges)
GRANITE
CLASS: Intrusive (Plutonic)
Color: grey crystals (Quartz), white (Plagioclase),
beige (Alkali Feldspar), black (Biotite,
Hornblende)
Grain size: typically coarse-grained (>1cm), with
well-define crystals
Composition: Qtz-Plag-Felds-Bio-Horn
Formation: Silica-rich magma, intruding through the Earth’s crust and cooling slowly
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B.
SEDIMENTARY ROCKS
CONGLOMERATE
/BRECCIA
CLASS:
Clastic/fragmental
Color: variable
Grain size: pebble clasts
(rounded or angular) in
sand, silt and/or clay
matrix
Formation: accumulation and deposition of varying sized particles/grains (i.e. cementation)
SANDSTONE
CLASS:
Clastic/fragmental
Color: variable
Grain size: 0.06-2mm
Occurs with faint or
prominent layering
Pinro
Formation: accumulation of sand-sized particles, and slow deposition of grains into layer
MUDSTONE/CLAYSTONE/SILTSTONE
CLASS: Clastic/fragmental
Color: variable
Grain size: silt=0.004-0.6mm, mud/clay=<0.004mm
(grains not seen by the naked eye)
H= ~1-2 (scratched by fingernail)
Formation*: Conglomerate/breccias, sandstones and mudstone/claystone/siltstone form
from “sedimentation” in a water body (eroded particles carried in suspension in the water,
then are slowly deposited and compacted by overlying pressure)
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SHALE
CLASS: Clastic/fragmental
Color: Dark grey
Grain size: composed of clay particles (grains not
seen by the naked eye)
A mudstone that is fissile (i.e. breaks along bedding
planes)
LIMESTONE
CLASS: Organic
Color: White
Reacts to HCl (only if
powdered)
Weathering from water
forms carbonic acid.
Common to have
uneven surfaces
leading to Karst
environment (seen in
picture on left)
Areagaad
Formation: composed of seafloor bed remains (micro shells), compressed under pressure
DOLOMITE/DOLOSTONE
CLASS: Crystalline
Color: light pink, but dark
grey weathered surface
Weathered surface shows
“Elephant skin texture”
H=3.5-4
Habit=crystalline form has
small saddle-shaped crystals
Little reaction to HCl
Bholna
Formation: low temperature, high salinity/sedimentary basins environments
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C. METAMORPHIC ROCKS
SLATE
CLASS: Low-grade
Color: Dark grey to black
Grain size: Aphanitic to fine-grained
Composition: clay with Qtz-Mus-Ill-Bio-Chl
Foliated, homogeneous
H= softer than glass
Parent rock = Shale
Formation: regional metamorphism (low T and P)
PHYLLITE
CLASS: Low-grade
Color: grey-green, but
reddish-brown weathered
surface
Grain size: fine-grained
Composition: Qtz-SerChl +/- Felds, Amp, Gar
High fissility
Nawli
Formation: regional metamorphism (greater T and P compared to Slate,
but less
thanShale
Schist)
Parent
rock=
(MICA) SCHIST
CLASS: Medium-grade
Grain size: fine
Composition: >50% platy
& elongated minerals with
Qtz-Felds-Micas-Chl-TalcHorn +/- Graphite, Garnet
Schistocity (from lamellar
mineral)
Classified according to
dominant mineral
Chopra
Formation: regional metamorphism (greater T and P compared to Phyllite, but less than Gneiss)
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GREEN SCHIST
CLASS: Medium-grade
Grain size: fine
Color: green to greyish-brown
Dominant mineral: Chlorite, whereas remaining
composition: >50% platy & elongated minerals
with Qtz-Felds-Micas-Talc-Horn
Common schistocity
minerals)
(sheen
from
lamellar
Formation: regional metamorphism (greater T and P compared to Phyllite, but less than Gneiss)
TALC SCHIST
CLASS: Mediumgrade
Grain size: very
fine
Color: white-grey
Dominant mineral:
Talc
Fibrous and
greasy texture
Areagaad
Formation: regional metamorphism (greater T and P compared to Phyllite, but less than Gneiss)
GNEISS
CLASS: High-grade
Grain size: coarsegrained
Color: white
(Plagioclase) and black
(Amphibole) segregation
of minerals
Typically
foliated/parallel layers
Doba
Parent rock= Granite
Formation: regional metamorphism (greater T and P compared to Schist)
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AUGEN GNEISS
CLASS: High-grade
“Augen” = eye-shaped
Grain size: coarse-grained
Color: white and black segregation of minerals
Eye-like crystals are pinched and ends are
stretched
Layers are folded
Parent rock= Granite
Formation: regional metamorphism (greater T and P compared to Schist)
QUARTZITE
CLASS: High-grade
Grain size: medium to
coarse-grained
Color: beige to pink, but
red due to iron oxide.
Weathered surface can be
dark grey
Typically non-foliated
Parent rock= Sandstone
Pinro
Pinro
Formation: Related to regional metamorphism
– high compression
Quartz grains re-crystallize and cement together to form interlocking mosaic of grains
MARBLE
CLASS: High-grade
Grain size: fine to medium-grained
Color: white to beige
Well-defined crystals have high luster
Typically non-foliated
Parent rock= Limestone or Dolostone
Formation: regional or contact metamorphism; recrystallized minerals (Calcite or Dolomite)
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SECTION 3: METAMORPHISM & ALTERATION
3.1 METAMORPHISM
There are 3 main types of metamorphism:
Regional: a large area of continental crust is involved in mountain range formation
(convergent plate boundaries) leading to extreme compression conditions
Contact: occurring around intrusive igneous rocks (ex. Granite). High temperature
gradient is produced locally around intruding magma.
Hydrothermal: High temperature environment where fluid (usually water or air)
interacts with pre-existing rock. Metasomatism occurs (i.e. chemical alteration of the rock
leading to the formation of new mineral assemblages).
3.2 ALTERATION
The two main types of alteration discussed in this section are physical and chemical
alteration. Physical alteration in rocks refers to a change in appearance, from folding (referred
to as “plastic” deformation) or faulting (referred to as “brittle” deformation). Deformation is
in reference to the degree of strain required to break the rock. Chemical alteration in rocks
describes a change in the mineral assemblage (i.e. different minerals are only stable at certain
pressure and temperature conditions). An explanation of the latter type of alteration can be
assisted by Figure 3.
Figure 3. Amphibolite to Greenschist reaction
The majority of rocks are subject to alteration, but in simpler terms, this often means that one
mineral is replaced by another due to a chemical reaction. Figure 3 shows that the mineral
assemblage present in the Amphibolite facies:
Garnet (gt) + Hornblende (hbl) + Plagioclase (plag)
Changes to the Greenschist facies with the mineral assemblage:
Chlorite (chl) + Actinolite (act) + Epidote (ep) is stable
Due to decreasing temperature, but constant pressure (as previously seen in Figure 2).
Another type of chemical alteration is silification and it occurs when the rock’s environment
is changed by the introduction of a Silica-rich fluid. This coats the pre-existing rock with this
fluid and thus, alters the hardness of the rock to be equivalent to that of Quartz (H=7).
15
In summary, the geology across the area where CHIRAG is presently working is very diverse
ranging from sedimentary environments to low- and high-grade metamorphism (see Table 4).
Table 4. Local geology around CHIRAG areas
Region
Main Geology
Spring type
Reetha
Phyllite, Quartzite, Schist
Fracture
Kasiyalekh
Phyllite, Quartzite, Gneiss
Fracture
Sualbaari
Phyllite, Quartzite, Schist
Contact, Fracture
Kathpuria
Limestone (Talc), Dolomite
Karst
Dewaldhar
Limestone, Dolomite, Phyllite
Karst
Pinro
Quartzite, Green Schist, Phyllite
Fracture
The different rock types in each area controls the type of the spring (called the structural
control). For example, fracture springs occur in rocks with a high tendency to break (i.e.
brittle deformation) and this leads to the formation of “joints” which are parallel or
perpendicular passages for water to pass through. Contact springs occur where overlying
rocks have varying integrities (i.e. one rock has higher permeability or higher brittle
deformation so water favors that pathway compare the other adjacent rock). In the case of
karst springs, the reaction of limestone with water forms carbonic acid, which carves
pathways in the rock where water easily flows.
Moreover, specific rock properties such as how sorted the grains are or the nature of fractures
play an extremely important role in terms of increasing the rock’s storativity of water. For
example, a well-sorted Sandstone (see Figure 4) has a higher storage capacity of water
compared to an unsorted Sandstone. On the other hand, a fractured Shale has a higher storage
capacity as the individual cracks form a large network where water can flow (an unfractured
rock has pockets of water which cannot be connected).
Figure 4. Sortedness of a Sandstone and Figure 5. Fractures in a Shale
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APPENDIX
Suggestions for geologic field tools:
http://www.geologysuperstore.com
1. Hand lens (18x magnification, 18-21mm viewing field)
Purpose: magnified view of microscopic minerals and features present in field specimen
Unit Price: ~ $5.00 USD
2. Dual magnetic pen & engineering tungsten scriber
Purpose: to determine magnetic properties and specific hardness of minerals & rocks
Unit Price: ~$8.00 USD (10% discount 10+ purchased, 40% discount 20+ purchased)
3. Metric protractor
Purpose: to measure angle and length of linear features (bedding, foliation) in rocks
Unit Price: ~$4.00 USD
4. Acid bottle (empty)
Purpose: to determine presence of carbonaceous minerals (fill with hydrochloric acid)
Unit Price: ~$1.00 USD
5. Field sample cards (grain size card or rock texture cards)
Purpose: pocket-sized cards with useful properties to compare to field specimens
Unit Price: ~$2.00-2.50 USD
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6. Streak Plates (white or black)
Purpose: to test the color of a mineral’s streak which is one method aiding in its identification
Unit Price: only come in packs of 10 for ~$5.00 USD
REFERENCES:
http://webmineral.com/ (rock properties)
Figure 1: http://everythingilearnincollege.blogspot.in/2011/02/introduction-to-minerals-androcks.html
Figure 2 & 3: http://en.wikipedia.org/wiki/Metamorphism
Figure 4 & 5: Dr. Jeffrey Mckenzie’s slideshow, McGill University lecture (2011)
2.2 MINERALS
Quartz
http://www.galleries.com/Quartz (Crystallie Quartz)
http://www.statesymbolsusa.org/Georgia/gem_quartz.html (Amorphous Quartz)
Orthoclase http://www.soes.soton.ac.uk/resources/collection/minerals/minerals/pages/M27-FeldsparO.htm
Albite http://www.minerals.net/image/1/12/albite.aspx
Biotite http://geology.about.com/od/minerals/ig/minpicmicas/minpicmicabiotite.htm
Muscovite http://geology.com/minerals/muscovite.shtml
Sericite http://wonderworlds.org/mineral/sericite.htm
Chlorite http://www.soes.soton.ac.uk/resources/collection/minerals/minerals/pages/M33-Chlorite.htm
Talc http://library.thinkquest.org/05aug/00461/talc.htm
Illite http://www.mindat.org/show.php?id=2011&ld=1
Hornblende http://www.geoprime.com/mineral/Image%20pages/hornblendeM350.htm
Calcite http://annagiiordano.blogspot.in/2010/03/michigan-minerals.html
Gypsym http://www.pitt.edu/~cejones/GeoImages/1Minerals/2SedimentaryMineralz/Gypsum.html
2.4 ROCKS
18
Basalt http://itc.gsw.edu/faculty/tweiland/igrx.htm
http://www.pitt.edu/~cejones/GeoImages/2IgneousRocks/IgneousCompositions/3Basalt.html
(Vesicular Basalt)
Granite http://geology.about.com/od/rocks/ig/igrockindex/rocpicgranite.htm
Conglomerate http://flexiblelearning.auckland.ac.nz/rocks_minerals/rocks/conglomerate.html
Breccia http://flexiblelearning.auckland.ac.nz/rocks_minerals/rocks/breccia.html
Sandstone (layered) http://www.minimegeology.com/home/mgeo/page_84)
Shale http://geology.com/rocks/sedimentary-rocks.shtml
Mudstone/Claystone/Siltstone
http://flexiblelearning.auckland.ac.nz/rocks_minerals/rocks/mudstone.html
Dolomite http://geology.about.com/od/more_sedrocks/ig/sedrocksgallery/dolomite.htm
Limestone http://sun-impex.com/limestone-sun-impex.htm
Slate http://www.solutionssealers.com.au/index.php?page=60&ssid=60&mid=4
Phyllite http://batuphyllite.blogspot.com/2012/04/batu-phyllite-melihan-foliated.html
Mica Schist http://geology.about.com/od/rocks/ig/metrockindex/rocpicschist.htm
Green Schist http://www.geol.umd.edu/~jmerck/geol100/lectures/17.html
Talc Schist http://geology.about.com/od/rocks/ig/metrockindex/rocpicsoapstone.htm
Gneiss http://www.geosci.ipfw.edu/PhysSys/Unit_4/metam.html
Augen Gneiss http://www.pitt.edu/~cejones/GeoImages/6MetamorphicRocks/Gneiss.html
Quartzite http://flexiblelearning.auckland.ac.nz/rocks_minerals/rocks/quartzite.html
Marble http://www.minimegeology.com/home/mgeo/page_482_22/marble_metamorphic_rock.html
*Remainder of photographs in this manual were taken by Sophia Yee
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