Metamorphic Rocks

Rock Cycle

Objectives

14 – Describe the types of changes associated with metamorphic rocks.

15 – Contrast regional and contact metamorphism.

Metamorphic Rocks

Pre-existing rocks changed by heat and pressure

Different Types of Changes

Compaction Grains move closer. Rock becomes more dense. Porosity reduced. Example: clay to shale to slate

Recrystallization- Growth of new crystals. No changes in overall

chemistry. New crystals grow from the

minerals already present Foliation

Minerals separate into bands New minerals form from heat

and pressure

Types of Metamorphism: Contact Contact (thermal)

Small scale Associated with igneous

intrusions

Types: Regional Metamorphism Regional (dynamic)

Large scale Associated with mountain

building

Foliated vs. Non-foliated

Foliated – has bands or layers

Non-foliated - No banding Form from rocks made

up of single minerals

Rank

The degree of metamorphism required to change a rock

Quartzite

Non-foliated Visible minerals grains Low-high

metamorphisis Quartz Parent - Sandstone

Marble

Non-foliated Usually visible grains –

granular Will effervesce in HCl Calcite Parent - Limestone

Anthracite

Non-foliated Black color Metamorphosed Coal

Peat→Lignite→

Bituminous coal→ Anthracite

Slate

Foliated Small grain size Low metamorphism Visible layering A metamorphosed

shale

Phylite

Foliated Small-visible grains Low-medium

metamorphism Sheen Crenulations- slight

wavy appearance A metamorphosed slate

Schist

Foliatied Visible grain size Medium metamorphism Biotite, Garnet A metamorphosed

phylite Basalt may change into

schist

Gneiss

Foliated Large visible grains High degree of

metamorphism Definite banding and

recrystallization Horneblende, Quartz Metamorphosed schist