Lecture 11 Flashcards
(32 cards)
What is a rock?
Any naturally formed solid material composed of one or more minerals and having some degree of chemical and mineralogical consistency
What are Igneous rocks?
Rocks formed from the solidification of molten matter either at the surface or subsurface.
What are the 2 groups of igneous rocks?
Intrusive: magma cools and crystallizes within earths crust
Extrusive-Magma cools and crystallizes at earths surface
What is characteristic of intrusive rocks?
All minerals making it up are visible with the unaided eye. Light minerals form acidicly in the crust, dark minerals are basic and formed in oceanic crust
What is characteristic of extrusive rocks?
Lava that crystallizes incredibly fast (less than 1 week), can’t see each mineral with the unaided eye as they didn’t have time to form.
What are the 4 types of igneous rocks (recognized by crystal sizes)
Phaneritic, Aphanitic, Glassy, and Fragmental
What are phaneritic rocks?
Occurs in INTRUSIVE rocks only. Crystals can be seen with unaided eye, slow cooling process
What are aphaneritic rocks?
Have small sized crystals that can be seen by making a thin section and looking at it under a microscope-indicates fast cooling (extrusive)
What are Glassy rocks?
Came from oceanic eruptions. Molten material crystallized incredibly rapidly, no time for elements to arrange selvses into slid crystalline component-amorphous rock (but some do have crystals)
Why do some glassy rocks have crystals (2 Ideas)
Calcite crystals are YOUNGER and placed themselves on rock OR
Calcite crystals are OLDER and embedded themselves in rock
What are fragmental rocks?
Consist of pyroclastic material ejected as lava from a volcano which falls down at the Earths surface as partlly consolidated rocks. Mixed characteristics between igneous and sedimentary.
What are the different textures of phaneritic rocks?
Granular, Porphyllitic, Poikilitic.
What does the granular texture demonstrate?
Slow cooling process, crystals had time to grow (But not enough time to become Euhedral). All minerals have comparable sizes but are Anhedral
What does the Porphyritic texture demonstrate?
Large sized minerals, occuring in the mantle of crust. Some are truly euhedral or subhedral. Time to grow and develop
What are the 2 types of porphyritic texture?
Phenocrysts-Large sized, time to grow and develop
Ground mass- fast forming, looks black as the background
What are the 2 phases of the Poikilitic texture?
1) large number of minerals-magma turns them homogenous
2) Small minerals that were formed first are caught in the mass of the larger and become homogenous
What are Plutons?
General term for body of intrusive rocks (igneous). Process of crystalization happens below ground.
What is a batholith?
Crystallized magma chamber that reaches the surface (HUGE)
What are stocks?
Also irregular structures that reached surface, but smaller than batholiths
What does it mean that stocks and batholiths are discordant?
They pass through preexisting rocks
What are the 2 most frequent intrusive igneous rocks?
Dike-fracture of igneous rocks cut through preexisting (discordant)
Sill- 2 rock boundaries are parallel, sill sits on top of other rocks (concordant). Sill is younger than rocks above and below
What type of igneous rock is volcanic?
Extrusive
What are basalts?
Volcanic igneous rocks-most frequent in the solar system
What are the 2 types of volcanic rocks?
Lava flows and pyroclastic flows
