Metamorphic rocks
These are formed from igneous and sedimentary rocks under the influence of heat, pressure, chemically active liquids and gases. Changes may occur in mineral composition of rocks or texture or both. The change due to water is called hydro metamorphism, due to heat is thermo metamorphism and due to pressure is called dynamo metamorphism.
Metamorphic rocks:- These rocks are classified according to their structure and parent material
1.Banded (foliated)
• Metamorphic rocks that have more or less parallel layers of different minerals.
• Usually uniformed in color or they have alternate light and dark-colored layers.
2.Non-banded
• Metamorphic rocks that have a random pattern of mineral crystals
• Any pre-existing rock may be the parent of metamorphic rock.
• Both igneous and sedimentary rocks are parent rocks.
Examples of Metamorphic rocks
Sand stone : Quartizite
Shale : Slate/mica, schist
Lime stone : Marble
Granite : granite gneiss
Dolerite : Hornblende gneiss
1. Gneiss
• Banded (alternates light and dark bands)
• Derived primarily from acidic igneous rocks.
• Contains an abundance of feldspar
2. Schists
• Layered • Fairly uniform in color
• These are metamorphosed shale, gneiss, or basic igneous rock.
• Newly formed minerals like mica, chlorite, and hornblende tend to predominate
3. Slate
• Layered • Derived from shale • Mineral grains are invisible
• Is more dense and compact than shale and cleaves into sheet
Slate
Quartzite
Gneiss
Schist
Marble
4.Quartzite • Non-layered metamorphosed sandstone
• Very hard
• Weathers extremely slowly
• The rock fractures through sand grains which are mainly quartz
5. Marble
• Is a recrystallized limestone with a random array of mineral grains
• Coarser-grained than parent limestone
• Weather more slowly than limestone
• The impurities determine the kind of soil.