Metamorphic Rock Lab

Whatever you do- don't take the schist for granite!

Assignment: Activity 7.1, pg. 167. Complete Metamorphic Rock Worksheet, pg. 169.

Metamorphism is the alteration of pre-existing rocks due to the effects of high ___________
and /or high ______________. Both the orginal rock's mineralology and __________ are affected in some cases. The rock is never ____________.

Types of Metamorphism

Contact Metamorphism- this causes alteration of existing rocks as the result of the tremendous ________ of a nearby _______________ intrusion. The alteration of the existing rock is greatest where it is _____________ to the boundary of the magma with the effect diminishing the further away you go. There is little to no direct pressure involved with this type of metamorphism.

Regional Metamorphism- this type of metamorphism is associated with the large scale movement and _______________ of the Earth's crust during a ____________ building event. Here, where tremendous forces are able to fold rock, the effects of metamorphism are due mostly to ____________.

Metamorphic Grade

Grade is the term given to the __________ of metamorphism. The more heat and/or pressure a rock undergoes, the higher the grade of metamorphic rock it produces.

Low grade to high grade rocks are slate- phyllite- schist (chlorite-mica-hornblende-garnet) - gneiss.

Texture and Composition of Metamorphic Rocks

The resulting rock having been altered by metamorphism is determined by three things:

1. The ___________ of minerals present in the original rock
2. The metamorphic processes involved
3. The ___________ of metamorphic process reached

Metamorphic rocks fall into two main texture categories- foliated and unfoliated.

Foliated metamorphic rocks are those which contain minerals showing a preferred alignment or ______________ and/or a segregation of light and dark minerals into distinct __________. These are typically formed by regional metamorphism.

Foliated textures

slaty- parallel orientation of ________________ platy grains.

phyllitic- barely ____________, platy grains in parallel to wavy orientation. The size and type of mineral present in this rock (usually _________) give it a characteristic sheen due to their alignment.

schistose- _____________ texture having minerals aligned in sub-parallel to parallel orientation. Metamorphic rocks having this type of foliation are typically composed of either __________ minerals such as mica or elongate minerals such as hornblende.

gneissic- coarse texture having minerals which have segregated into light and dark ___________. Generally, the composition of these light and dark bands are each dominated by one or two minerals, the light typically of ___________ and feldspar, the dark typically of hornblende and _________ mica.

granulitic- coarse, __________-grained texture characterized by either quartz, feldspars and garnet or by pyroxene. Foliation is typically more subtle in this type of texture.

 

Non-foliated metamorphic rocks are those containing minerals which do not show ___________ or preferred ______________. These are typically formed by contact metamorphism.

Non-foliated textures

dense- having an ultra _________-grained texture

crystalline- composed of coarse, _____________ crystals

granular- having a __________-grained, sugary texture.

Other terms

porphyroblast- a large mineral ____________ having developed in a rock due to metamorphic recrystallization. Some minerals, such as garnet, only occur as prophyroblasts in metamorphic rocks.

Protolith- what the ____________ rock was prior to metamorphism