Wavy bands of dark minerals visible in gneiss bedrock probably formed from the (1)
cementing together of individual mineral grains
(2) cooling and crystallization of magma (3) evaporation of an ancient ocean (4) heat and pressure during metamorphism.
What causes banding in minerals?
The banding is usually due to the
presence of differing proportions of minerals in the various bands
; dark and light bands may alternate because of the separation of mafic (dark) and felsic (light) minerals. Banding can also be caused by differing grain sizes of the same minerals.
What type of rock is most likely to have wavy bands of light and dark minerals in it?
Wavy bands of light and dark minerals visible in
gneiss bedrock
probably formed from the 5.
What rock has light and dark banding?
Normally, the presence of light and dark band of
gneiss
is due to the seggregation of felsic and mafic mineralization. The alternating darker and lighter bands in Gneiss are because of mafic and felsic minerals therein.
What are the factors could cause a change in texture and mineral composition of rocks?
During metamorphism the mineral content and texture of the protolith are changed due to
changes in the physical and chemical environment of the rock
. Metamorphism can be caused by burial, tectonic stress, heating by magma, or alteration by fluids.
What is the difference between banding and mineral alignment?
This parallel alignment causes the
rock to split easily into thin layers or sheets
. Foliation is common in aphanitic as well as phaneritic metamorphic rocks. … Banding means that the rock consists of alternating, thin layers (typically 1 mm to 1 cm) of two different mineral compositions.
What type of rock has wavy layers?
| Characteristics Minerals Rock Name | Thick bands, wavy, semi-continuous layers of white quartz, feldspar, and mica Medium to coarse-grained Banded, coarsely crystalline Large, crystalline grains Feldspar Quartz Mica Hornblende Garnet Gneiss |
|---|
What type of rock is diorite?
| Type Igneous Rock | Texture Phaneritic (Coarse-grained) | Origin Intrusive/Plutonic | Chemical Composition Intermediate | Color Approximately half dark, half white minerals |
|---|
What rock type is Obsidian?
Rondi: Everyone, meet Obsidian , an
igneous rock
that from melted rock, or magma. Obsidian is an “extrusive” rock, which means it is made from magma that erupted out of a volcano. If it was an igneous rock that formed from magma underground and did not erupt, it would have been called an “intrusive” rock.
What type of rock is chalk?
Chalk,
a sedimentary rock
, is a soft form of limestone that is not well cemented and thus is often powdery and brittle.
What rock has no layers?
Basalt has large crystals because it cools slowly. Other
igneous rocks
cool so quickly that gas from the magma doesn’t have time to escape into the air before the magma turns solid. This leaves some igneous rocks, like scoria, with holes or spaces in them. Igneous rocks rarely contain fossils and are not layered.
How can you tell if a rock has layers?
Layers: Layers in rocks show in different ways. In some rocks
different colored minerals are lined up in ribbons
.. Usually there are two colors, often black and white, or green and white, of black and tan or pink. Ribbon like layers are found in the rock, gneiss.
How can you tell if it is a metamorphic rock?
Metamorphic rocks are rocks that have become changed by intense heat or pressure while forming. One way to tell if a rock sample is metamorphic is
to see if the crystals within it are arranged in bands
. Examples of metamorphic rocks are marble, schist, gneiss, and slate.
What does the presence of Hornfels reveal?
It reveals that
the rock has undergone metamorphism at a shallow depth and have been transformed due to heating by igneous masses through contact metamorphism
.
What are the 3 characteristics of metamorphic rocks?
- Classified by texture and composition.
- Rarely has fossils.
- May react with acid.
- May have alternate bands of light and dark minerals.
- May be composed of only one mineral, ex. marble & quartzite.
- May have layers of visible crystals.
- Usually made of mineral crystals of different sizes.
- Rarely has pores or openings.
What are the two factors that control the mineral composition of metamorphic rock?
Temperature and pressure
are important factors in determining the new minerals that form in a metamorphic rock. Different minerals form under different pressure and temperature conditions.
