ROCKS:
RECORDS
OF
GEOLOGIC
PROCESSES
(地質作用的紀錄)
ROCK, by definition,
is composed of an aggregate of minerals
(原素)
(礦物)
(岩石)
• Appearance of a rock is related to:
1. Mineralogy = types and relative proportions of constituent
minerals
2. Texture = size, shape and orientation of mineral grains
• These features relate to the origin and history of the rock.
When many rocks are understood, the geologic history (and
tectonic setting) of a region can be inferred.
Where do we see rocks?
• Not on the
surface of course!
• They are at
depth in most
places covered by
soil and regolith
(風化層).
Three general rock types:
1. Igneous - formed by solidification of molten
rock (>700°C)
2. Sedimentary - formed as burial products of
sediments, on land or sea
3.Metamorphic - formed by transformation in
the solid state of pre-existing rock due to
changing pressure and temperature.
(火成岩)
(沉積岩)
(變質岩)
Sedimentary rocks
comprise a
majority of the
surface of the
Earth, but are a
minor volume of
the total volume of
the crust.
IGNEOUS ROCKS (火成岩)
Definition: A rock formed by the solidification of magma
(molten rock)
Igneous environments
IGNEOUS ROCKS (火成岩)
• Can be intrusive (crystallizing below the surface of
the Earth) or extrusive (crystallizing at the surface
of the Earth)
• Textures in igneous rocks relates
to the composition of the magma,
rate of cooling of the magma and
any flow features of the magma
• Extrusive (噴出) rocks - rapid
cooling, therefore fine-grained or
glassy; some surface flows
• Intrusive (侵入) rocks - slower
cooling, therefore coarser grained;
flow features possible

IGNEOUS ROCKS (火成岩)
SEDIMENTARY ROCKS (沉積岩)
Definition: A rock formed by the accumulation and
cementation of mineral grains by wind, water or ice
transportation to the site of deposition, or by chemical
precipitation at the site.
Typical sedimentary
depositional environments
• Sedimentary
rocks - generally
characterized by
bedding i.e.
parallel layers of
sediments
• Textures of
sedimentary
rocks relate to
the manner of
sediment
transport and
deposition e.g.
high vs. low
velocity
transport
• This is an
interface
between the
atmosphere,
hydrosphere
and lithosphere.
SEDIMENTARY ROCKS (沉積岩)
• Types:
1. Clastic - physically deposited sedimentary particles
(clasts - broken rocks, remains or products of animals or
plants) transported and laid down by running water,
wind or ice. Generally silicate minerals.
2. Chemical and biochemical sediments
-chemical precipitation of dissolved
components of rocks at the
depositional site e.g. halite, calcite
3. Mixtures of both of the above
• Lithification of sedimentary rocks –
hardening into a solid rock due to
compaction and cementation

METAMORPHIC ROCKS (變質岩)
Definition: A rock whose original mineralogy, texture, or
composition has been changed by the effects of pressure,
temperature, or the gain or loss of chemical components.
• Occurs between temperatures of roughly 250°C (end of
sedimentary lithification processes) and melting of the rock
(>700°C)
Contact and regional metamorphism
at plate-collisional mountain ranges
Burial metamorphism in
deep sedimentary rocks
Cataclastic metamorphism
along faults
Contact and regional
metamorphism at
subduction zones
Hydrothermal metamorphism
at mid-oceanic ridges
METAMORPHIC ROCKS(變質岩)
• General classification of type of metamorphism relates to
location of heat source
1. Regional metamorphism - heat
source in not apparent, but
generally higher; associated with
mountain building episodes
extending over large regions
2. Contact metamorphism - heat
source is apparent i.e. associated
with intrusion of a magma that
"cooks" the surrounding rocks
• Textures relate to the pressure,
temperature and deformational
history of metamorphic rock

Metamorphic environments
THE ROCK CYCLE (岩石循環)
• Inter-relationships among the three rock types
• The rock cycle is directly related to plate tectonics (板
塊構造) - in turn, the rocks that we currently see can infer
tectonic conditions in the past.
• This is an
interaction
among the
atmosphere,
hydrosphere,
lithosphere and
asthenosphere
(the mantle
layer) and is
unique to Earth
Recommended Web-sites:
Chinese web-site:
岩石圈
English web-sites:
Discover How Rocks Are Formed
Rocks For Kids
Your Gemologist
Rockdoctors Guide to Minerals, Igneous, Metamorphic, and Sedimentary
Rocks