 Metamorphism literally means to “ change form
.”

The degree of metamorphism is reflected in the rocks texture and mineralogy.
METAMORPHISM CHANGES TEXTURE

Two textures are formed as a result of metamorphism;
1) Foliated Texture
2) Non-Foliated Texture
Reference:
Tarbuck and Lutgens
Pages

1) Allignment of minerals.

Directional stress causes minerals to align when recrystallizing. The orientation of these minerals is usually perpendicular to the compressional forces.

This gives the resulting metamorphic rock a layered appearance.

This is common during high-grade metamorphism and often produces a foliated texture . Example: Gneiss.
Gneiss

2) Recrystallization of minerals.

Pressure causes minerals to recrystallize which generally forms larger, more dense crystals.

The recrystallization process causes some metamorphic rocks to display visible crystals with no visible evidence of the original mineral grains. For example, quartz sandstone changes to form quartzite.
Quartz
Sandstone
Recrystallizes
Quartzite

This is common during low-grade metamorphism and often produces a non-foliated texture .

1) Foliated (i.e. layered or banded)
2) Non-foliated .
• Note that the texture of a metamorphic rock is usually coarser than the parent rock (i.e. previous rock).
Foliated Non-foliated

Two textures are formed as a result of metamorphism;
1) Foliated Texture

Results when the minerals of a rock are brought into parallel alignment during recrystallization. Produces a banded or layered appearance.
Before
Metamorphism
After
Metamorphism

Granite when metamorphosed forms Gneiss.
Examples:
Slate, Phyllite,
Schist & Gniess

Two textures are formed as a result of metamorphism;
2) Non Foliated Texture

Results when the minerals of a rock are recrystallized creating uniform sized crystals with no visible foliation.

This occurs when limestone (consist of pure calcite) undergoes metamorphism and the smaller calcite crystals combine to form larger interlocking crystals. This process of recrystallization of calcite forms Marble .
Marble
Examples:
Quartzite &
Marble

(Sedimentary)
Changes to
(Sedimentary)
Changes to
(Sedimentary)
Changes to
(Phyllite – Schist - Gniess)
(Igneous)
Changes to

Using examples, distinguish between foliated and non-foliated metamorphic rocks.
Answer:
Foliated: show layering or banding of different minerals created by the alignment of minerals during directional stress and recrystallization (Ex: schist, gneiss)
Non foliated: a mass or network of interlocking crystals consisting of one mineral with no visible layering or banding (Ex: marble, quartzite)