METAMORPHIC LECTURE 4

 

Important points to note when looking at metamorphic rocks in their protolith groups:

a. Tremolite - actinolite is solid solution: FeMgsilicate vs CaMg silicate

b. Difference between staurolite and andalusite (in their cross sections)

c. Ultramafic rocks can be light-colored, pelitic rocks can be dark-colored

d. Andalusite being replaced by sillimanite

e. Calcsilicate rocks - diopside, garnet, etc. (epidote can be in skarns)

 

Metamorphic textures and structures - read text and read lab manual

 

NAMING METAMORPHIC ROCKS

Terminology:

blasto in prefix - relict tecture, i.e. blastoporphyritic

blasto in suffix - texture produced by met. , i.e. porphyroblastic

Names: [color] [texture] [mineralogy - least to most abundant] [root name]

Root names:

BANDING PRESENT

Gneiss

NO BANDING PRESENT

A. If no foliation present

Hornfels (fine grained equant)

Granofels (coarse grained equant)

Marble

Quartzite

B. If foliation present

Slate

Phyllite

Schist

Mylonite

Modification of root name:

In this class: Same as Lab manual (p. 114):

Mineralogy (least to most abundant) followed by root name, with any distinctive textural descriptors first (or even color first if it is distinctive).

Examples:

Porphyroblastic muscovite chlorite schist

Garnet hornfels

Nematoblastic actinolite talc schist