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Chapter 2 Rock第二章 岩石
Since minerals are the building blocks of rocks, it is
important that you learn to identify the most common
varieties. Minerals can be distinguished using various
physical and/or chemical characteristics, but, since
chemistry cannot be determined readily in the field, the
physical properties of minerals are used to identify
them.
§2-1: The main minerals in the rock( 造岩矿物 )
♥ Crystal form (晶形)
♥ Hardness (硬度)
(relative to a steel blade or you finger nail),
♥ colour( 真色,假色,它色 )
♥ Luster (光泽)
♥ Streak ( 条痕 )
(the colour when a mineral is ground to a powder).
♥ cleavage (解理)
Physical properties of minerals includefeatures such as :
Quartz is hard - it can easily scratch a steel knife blade. In many rock
s, quartz grains are irregular in shape because crystal faces are rare
and quartz does not have a cleavage(ie, it does not break on regular
flat faces).
1 Quartz( 石英 ):
Quartz is a glassy looking, transparent or t
ranslucent mineral which varies in colour f
rom white and grey to smoky. When there
are individual crystals they are generally c
lear, while in larger masses quartz looks
more milky white. 油脂光泽
Feldspar is also hard but can be scratched by quartz. Feldspar in ign
eous rocks (火成岩) forms well developed crystals which are roughl
y rectangular in shape, and they cleave or break along flat faces. The
grains, in contrast to quartz, often have straight edges and flat rectang
ular faces, some of which meet at right angles.
2 Feldspar (长石) :
Feldspar is the other common, light-coloured rock-forming m
ineral. Instead of being glassy like quartz, it is generally dull
to opaque (不透明) with a porcelain-like appearance. Col
our varies from red, pink (orthoclase 正长石 ), and white to
green, grey (plagioclase 斜长石 ).
Plagioclase斜长石
Orthoclase正长石
The most common amphibole is h
ornblende (角闪石) . Hornblen
de is quite similar to augite (普通
辉石) in that both are dark mine
rals, however hornblende crystals
are generally longer, thinner and
shinier than augite and the minera
l cross-sections are diamond-sha
ped.
hornblende (角闪石)
3 Amphibole (闪石)
The most common pyroxene mineral
is augite. Augite is generally dark gre
en to black in colour and forms short,
stubby (短而粗) crystals which, if
you look at an end-on section, have s
quare or rectangular cross-sections.
Pyroxene (辉石)
4 Pyroxene 辉石
Talc occurs in granular (粒状的)
or foliated (片状的) masses so
metimes known as soapstone (皂
石) . It is white to green, sometim
es grey or brownish. It is very soft a
nd will be scratched by a finger nail.
It has a greasy feel (滑感)
5 Talc (滑石)
Olivine in the jewellery trade, is ye
llow-green, translucent (半透明的) and glassy looking. Crystals
are not common; it usually occurs
as rounded grains in igneous (火成的) rocks or as granular mass
es. Olivine is almost as hard as qu
artz; it does not have a well-develo
ped cleavage.
6 Olivine 橄榄石
Mica is easily distinguished by i
ts characteristic of peeling into
many thin flat smooth sheets or
flakes (薄片) . This is similar
to the cleavage in feldspar exc
ept that in the case of mica the
cleavage planes are in only on
e direction and no right angle f
ace joins occur. Mica may be w
hite and pearly or dark and shi
ny .
7 Mica 云母
8 Gypsum (plaster stone, 石膏 )
9 Kaolinite ( 高岭石 )
10 Montmorillonite (蒙脱石)
11 Water mica (伊利石)
§2-2: Rock( 岩石 )( 一种或多种矿物组成的集合体 )
一 、 The classification of rock according to the cause of formation
igneous rock (岩浆岩)
(magma rock)
sedimentary rock (沉积岩)
metamophic rock (变质岩)
岩石
二、 Igneous rock
1 the formation of igneous rock: Deep within the Earth, rock is kept in a molten (融熔
的) state due to extreme temperature and pressure.
This molten rock is called magma (岩浆) . The mag
ma is constantly moving and sometimes moves its wa
y to the surface through the cracks (裂缝) in the soli
d rock. Once it reaches the surface, it is called lava
(熔岩) .
The location it pushes through to the surface is call
ed a volcano (火山) . The opening in the volcano
that the lava erupts out of is called a vent( 出口 ). Fo
r many volcanos, there is more than one vent. Ofte
n volcanos have a funnel (漏斗) shape with a pit
at the top. This pit is called a volcanic crater (火山
口) . If this crater becomes very large, the walls of
the crater might collapse to produce a feature called
a caldera (喷火山口)
How Igneous rock rock Is FormedPyroclastic ash( 火山灰 )
Batholith岩基 Captive mass
俘虏体
laccolith岩盘
岩墙Rock wall
岩株
Volcano neck
火山颈
Lava flow岩流
2 the formation state of igneous rock(岩浆岩的产状)
Sill 岩床
3 the classcification of igneous rock (岩浆岩的分类)
( 1 ) According to the formation state( 按产状 )
◈Intrusive Igneous Rocks (侵入岩) - usually medium to coarse grained texture due to slow cooling. Typically light coloured. ◈ Extrusive Igneous Rocks (喷出岩) - glassy or fine-grained due to rapid cooling. May have voids due to degassing of the magma. Typically dark coloured.
(2) According to the Silica Content and Mineral Composition( 根据二氧化硅含量 )
◈ Acid Igneous Rocks( 酸性岩 ) - silica rich ( > 65% by weight) composed mainly of light coloured minerals (eg. feldspars, quartz)
◈ Intermediate Igneous Rocks (中性岩) - silica 50-65% by weight, composed mainly of feldspars, some mafic (铁镁质的 minerals, with some quartz.
◈ Basic Igneous Rocks (基性岩) - silica poor ( < 50% by weight) contain significant
amounts of mafic or dark coloured ferromagnesian mineral
s (eg. olivines, pyroxenes, amphiboles, micas). No free qua
rtz.
3the description of main igneous rock (岩浆岩描述)
◈ granite (花岗岩)
Granite is an igneous rock that is composed of four
minerals. These minerals are quartz, feldspar, mica, a
nd usually hornblende. Granite forms as magma cools f
ar under the earth's surface. Because it hardens deep u
nderground , it cools very slowly. This allows crystals
of the four minerals to grow large enough to be easily s
een by the naked eye.
Granite is an excellent material for building bridges and
buildings because it can withstand thousands of pounds of pressure.
It is also used for monuments because it weathers slowly.
Engravings in the granite can be read for hundreds of years, making
the rock more valuable.
Granite is quarried in many places in the world including the
United States. The State of New Hampshire has the nickname
"Granite State" because of the amount of granite in the mountains of
that beautiful state. The Canadian Shield of North America contains
huge outcroppings (surface rocks) of granite.
◈ porphyritic granite ( 花岗斑岩 )
shallow intrusive rock (浅成侵入岩) moderate crystallization (中等结晶) porphyritic structure 斑状结构 quartz-feldspar-black mica
花岗斑岩
◈ rhyolite (流纹岩)
Rhyolite is very closely related to granite. The difference is r
hyolite has much finer crystals. These crystals are so small th
at they can not be seen by the naked eye. Rhyolite is an extru
sive igneous rock having cooled much more rapidly than granit
e, giving it a glassy appearance. The minerals that make up rh
yolite are quartz, feldspar, mica, and hornblende.
Rhyolite流纹岩
◈ Diorite ( 闪长岩 )
1 abyssal intrusive rock2 well crystallization 3 feldspar, quartz, amphibole
◈ Diorite porphyrite (闪长玢岩)
1 shallow intrusive rock,2 median crystallization 3 feldspar, quartz amphibole
Dacite is an extrusive igneous rock. The principle minerals that make up dacite are plagioclase, quartz, pyroxene, or hornblende. Dacite
安山岩
◈ Dacite (安山岩)
Andesite
◈ pyroxenire ( 辉岩 )
1 abyssal intrusive rock2 well crystallization 3 amphibole, phyroxene feldspar
Basalts are dark colored, fine-gra
ined extrusive rock. The mineral gra
ins are so fine that they are impossi
ble to distinguish with the naked ey
e or even a magnifying glass (放大镜) . They are the most widesprea
d of all the igneous rocks. Most bas
alts are volcanic in origin and were f
ormed by the rapid cooling and hard
ening of the lava flows. Some basalt
s are intrusive having cooled inside
the Earth's interior.
◈ basalt 玄武岩
1 ultrabasic rock (超基性岩石) (sio2<45%)
2 abyssal intrusive rock (深成岩) 3 well crystallization (结晶好) 4 olivine ; pgroxene
◈ olivine rock( 橄榄岩 )
◈ Obsidian 黑耀岩
Obsidian is a very shiny nat
ural volcanic glass. When o
bsidian breaks it fractures wit
h a distinct conchoidal (贝壳状的) fracture. Notice in
the photo to the left how it fr
actures. Obsidian is produced
when lava cools very quickly.
The lava cools so quickly th
at no crystals can form.
When people make glass they melt silica rocks like sand and quartz then cool it rapidly by placing it in water. Obsidian is produced in nature in a similar way.
Obsidian is usually black or a very dark green, but it can also be found in an almost clear form.
Pumice is a very light colored, frothy (起泡的) volcanic r
ock. Pumice is formed from lava that is full of gas. The lava is e
jected and shot through the air during an eruption. As the lava h
urtles (急飞) through the air it cools and the gases escape le
aving the rock full of holes.
◈ Pumice (浮石)
Pumice is so light that it actually floats on water. Huge
pumice blocks have been seen floating on the ocean after
large eruptions. Some lava blocks are large enough to
carry small animals.
三、 sedimentary rock (沉积岩)
1 the formation of sedimentary rock: For thousands, even millions of years, little pieces of our
earth have been eroded--broken down and worn away by
wind and water. These little bits of our earth are washed
downstream where they settle to the bottom of the rivers,
lakes, and oceans. Layer after layer of eroded earth is
deposited on top of each. These layers are pressed down
more and more through time, until the bottom layers slowly
turn into rock.
How Sedimentary Rock Is Formed
Sediments are subdivided into three types: ▦1 Clastic or detrital sediments (碎屑岩) Comprising particles of various sizes carried in suspension by wind, water or ice. Sand ( 砂岩 )is an example of a clastic sediment. Silt (粉砂岩) and sand size particles are carried in suspension by wind, water and ice.
2 the classification of sedimentary rock:
▦2 Chemical or precipitated sediments (化学岩)
which are carried in aqueous solution. Salt (halite) is a
n example of a chemical precipitate.
▦3 Organic or biogenic sediments (有机岩)
precipitated or accumulated by biological agents. Man
y organisms promote the precipitation of calcite to form b
iogenically precipitated calcareous (含钙的) muds.
3 The texture and structure of sedimentary rock 沉积岩的结构和构造
沉积岩的层理构造
平行层理
斜层理
波状层理
印模
粒序层理
交叉层理
沉积岩的结构特征
砂粒 孔隙 胶结物
砂粒
粘粒粉粒
铁饼形的
Sphericity 球形度[ sfe’risiti ]
4 the description of sedimentary rock
Conglomerate rocks are sedimentary ro
cks. They are made up of large sedimen
ts like sand and pebbles (鹅卵石) . T
he sediment is so large that pressure al
one cannot hold the rock together; it is a
lso cemented together with dissolved mi
nerals.
◈ gravel stone (conglomerate) 砾岩 (clastic rock)
◈ sand stone (d=2-0.05mm) 砂岩
Sandstone rocks are sedimentary rocks
made from small grains of the minerals
quartz and feldspar. They often form in
layers as seen in this picture. They are
often used as building stones.
◈ silt stone(d=0.05-0.005mm) 粉砂岩
◈ mud stone (d<0.005mm) 泥岩
kaolinite( 高岭石 )
montorillonite (蒙脱石)
water mica (伊利石)
Mineral Composition
Shale rock is a type of
sedimentary rock formed
from clay that is
compacted together by
pressure. They are used
to make bricks
◈ shale stone(d<0.005mm) 页岩
Limestone rocks are
sedimentary rocks that are made
from the mineral calcite which came
from the beds of evaporated seas
and lakes and from sea animal
shells. This rock is used in concrete
and is an excellent building stone for
humid regions. color grey
◈ lime stone 石灰岩
◈ dolomite rock 白云岩
color: white-grey
mineral: dolomit
◈ Gypsum 石膏
Gypsum rocks are sedimentary rocks made up of sulfate
mineral and formed as the result of evaporating sea water in
massive prehistoric basins. It is very soft and is used to make
Plaster of Paris, casts, molds, and wallboards.
四、 Metamorphic rock (变质岩)
Metamorphic rocks are generated by recrystalliz
ation of either igneous or sedimentary rocks by th
e action of any or all of the following: Pressure, T
emperature, Pore Fluids.
The type of metamorphic rock is determined by the parent ro
ck (母岩) and the P/T conditions.
In general, metamorphism causes:
Growth of new minerals
Deformation and rotation of mineral grains
Recrystallization of minerals as larger grains
1 the formation and classification of Metamorphic rocks
变质岩的形成
接触变质岩的形成
区域变质岩的形成
2 the description of Metamorphic rocks
◈ Marble (大理岩)
Marble is metamorphosed
limestone or dolomite. Both
limestone and dolomite have a
large concentration of calcium
carbonate (CaCO3). Marble
has many different sizes of
crystals.
Marble has many color variances due to the impurities
( 杂质 ) present at formation. Some of the different colors
of marble are white, red, black, mottled and banded, gray,
pink, and green.
Marble is much harder than its parent rock. This allows it
to take a polish which makes it a good material for use as
a building material, making sink tops, bathtubs, and a car
ving stone for artists. Today, headstones are made from
marble and granite because both of these rocks weather
very slowly and carve well with sharp edges.
◈ Quartzite (石英岩)
Quartzite is composed of sandstone that has been metamorphosed. Quartzite is much harder than the parent rock, sandstone. It forms from sandstone that has come into contact with deeply buried magmas. Quartzite looks similar to its parent rock. The best way to tell quartzite from sandstone is to break the rocks. Sandstone will shatter into many individual grains of sand while quartzite will break across the grains.
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