Interlude A: Introducing rocks
A.1 Introduction
Why are there so many distnct types of rocks? Many diferent processes can produce rocks, and
many diferent materials can form rocks ecause of the relatonship between rock type and the
process of formaton, rocks provide a record of geologic events of the Earth’s history and give insight
into interactons among components of the Earth System
A.2 What is Rock?
Rock: is a coherent, naturally occurring solid that consists of an aggregate of minerals or, less
common, a body of glass
Coherent: it must be broken in order to be separated They can form clifs pile of
unatached mineral grains does not consttute a rock
Naturally occurring: formed by natural processes
An aggregate of minerals or a body of glass: almost every rock consists of an aggregate of
many mineral grains/crystals From volcanoes rock types consists glass, occur either as
homogeneous body or as an accumulaton of tny shards
Grain: a more general term that can refer to a piece of mineral, to a fragment broken of a once
larger piece of mineral or of a pre-existng rock, or to a fragment of glass
Crystal: contnuous piece of a single mineral tat grew to its present shape may display crystal faces (aa
large crystal, or aggregate of crystals, of a single mineral may be called a mineral specimen, even if its
meters long )
What keeps a rock together?
Clastic rocks: grains held together by cement -> minerals that precipitated from water in the
space between grains
Crystalline rocks: crystals interlock with eachother
Glass is coherent because hot when welted together, or because it originated as contnuous mass
Rock is a volume of chemicals Every rock consists of other chemicals Granite (aoxygen, silicon,
aluminium, potassioum, sodium, calcium, iron and magnesium) Marble (aoxygen, carbon, calcium) In
both elements are incorporated in minerals Granite (aquartz, feldspar, mica, pyroxene, amphibole)
Marble mainly calcite
Oxygen and silicon are most common elements in rocks Silicate minerals t the Earth’s surface rock
occurs eiter as broken chunks that fell down a slope and/or were transported Or as bedrock (a that is
stll atached to the crust) exposure of bedrock is called outcrop. uildings rather build on strong
bedrock than on loose sediments
A.3 The basis of rock classifcation
braham Werner divided rocks in three categories (aprimary, secondary, tertary), most rock
formaton as a process that only took place in water, they were known as the Neptunists
James Huton’s group came to be known as Plutponists, afer the God of the underworld, because
they favored the idea that the formaton of certain rocks involved melts that has risen from deeper
within the Earth
A.1 Introduction
Why are there so many distnct types of rocks? Many diferent processes can produce rocks, and
many diferent materials can form rocks ecause of the relatonship between rock type and the
process of formaton, rocks provide a record of geologic events of the Earth’s history and give insight
into interactons among components of the Earth System
A.2 What is Rock?
Rock: is a coherent, naturally occurring solid that consists of an aggregate of minerals or, less
common, a body of glass
Coherent: it must be broken in order to be separated They can form clifs pile of
unatached mineral grains does not consttute a rock
Naturally occurring: formed by natural processes
An aggregate of minerals or a body of glass: almost every rock consists of an aggregate of
many mineral grains/crystals From volcanoes rock types consists glass, occur either as
homogeneous body or as an accumulaton of tny shards
Grain: a more general term that can refer to a piece of mineral, to a fragment broken of a once
larger piece of mineral or of a pre-existng rock, or to a fragment of glass
Crystal: contnuous piece of a single mineral tat grew to its present shape may display crystal faces (aa
large crystal, or aggregate of crystals, of a single mineral may be called a mineral specimen, even if its
meters long )
What keeps a rock together?
Clastic rocks: grains held together by cement -> minerals that precipitated from water in the
space between grains
Crystalline rocks: crystals interlock with eachother
Glass is coherent because hot when welted together, or because it originated as contnuous mass
Rock is a volume of chemicals Every rock consists of other chemicals Granite (aoxygen, silicon,
aluminium, potassioum, sodium, calcium, iron and magnesium) Marble (aoxygen, carbon, calcium) In
both elements are incorporated in minerals Granite (aquartz, feldspar, mica, pyroxene, amphibole)
Marble mainly calcite
Oxygen and silicon are most common elements in rocks Silicate minerals t the Earth’s surface rock
occurs eiter as broken chunks that fell down a slope and/or were transported Or as bedrock (a that is
stll atached to the crust) exposure of bedrock is called outcrop. uildings rather build on strong
bedrock than on loose sediments
A.3 The basis of rock classifcation
braham Werner divided rocks in three categories (aprimary, secondary, tertary), most rock
formaton as a process that only took place in water, they were known as the Neptunists
James Huton’s group came to be known as Plutponists, afer the God of the underworld, because
they favored the idea that the formaton of certain rocks involved melts that has risen from deeper
within the Earth
