Download Metamorphic Rocks

Metamorphic Rocks
Metamorphic means “change in form”.
Metamorphic rocks form from the
chemical and physical alterations of
pre-existing igneous or sedimentary
rocks. This is done by subjecting these
rocks to conditions of great heat and
pressure and chemical activity.
Main effects upon rocks
• The heat, pressure and chemical
activity will effect the metamorphic
rock’s:
1. Mineralogy – a new mineralogy will
form
2. Texture – the rock texture will alter.
Classification of Metamorphic rocks
• There are two classes of metamorphic
rocks.
• Contact (thermal) – these form when an
igneous intrusions are injected into the crust.
Heat from the magma metamorphoses
(changes) the surrounding rock forming a new
metamorphic rock
• Regional Metamorphic Rocks – these
rocks form over millions of years and many
thousands of meters of sediments
accumulated in the ocean basins. The
overlying weight causes the sediments to
lithify and eventually metamorphose.
• Example shale metamorphoses into slate
Agents of Metamorphism
•The agents of change
for metamorphic rocks
are:
•Heat, pressure and
chemical activity
Identification clue
These rocks are difficult to identify because remember
they used to be another kind of rock but because of
high heat and pressure they look bent, twisted, tortured
and or cooked. They tend to be dense and very hard.
They some times show banding like when a granite
metamorphoses to gneiss.
Identification clue
• Sometimes the flat minerals like mica all line
up parallel to each other due to extreme
pressure. This is called schistosity and the rock
is called a schist.
Identification Clue
• Metamorphic Rocks are:
•“Fubars”
• That is they are:
fouled up beyond all recognition