![]() ![]() Question 6: OK, let's do a thought exercise:Ĭhondrites are formed from the solids which condensed out of the Solar Nebula, the dust and gas and debris in orbit around the newly ignited Sun. Now For the Question: Look at the Brown glass pictures, and the various chondrule pictures, and describe for me the conditions under which chondrules actually form! If they do crystallize at all, they form Quench Crystals: long, delicate crystals that grow suddenly when the glass freezes, sorta like the rock version of snowflakes. In the frictionless vacuum of space they form tiny spheres, and the Quench Cool (i.e., they freeze very rapidly) upon eruption. Lunar Brown Glass is droplets of molten rock formed either through violent volcanic eruptions, or during melting events related to large meteor impacts. Question 5: Look at the pictures below: These are images of Lunar Brown Glass collected on the Apollo 17 Moon mission. Question 4: Describe the textures you see in the Chondrules: are they Crystalline or Clastic? Some of these types of chondrules are not perfectly round. In these chondrules, the pyroxenes form bladed or blocky grains. More common than the other kinds are Porphyritic Pyroxene chondrules. The pictures represent three different orientations of the slide, showing how the passage of light through the pyroxene crystals undulates as a function of crystal orientation. The five crossed polars pictures above show us a Radiating Pyroxene chondrule, with a beautiful fanning array of pyroxene crystals. The round ones with banded crystals in them, like a washboard, are called Barred Olivine Chondrules. Several different varieties of chondrules may be found in a chondrite. ![]() These are common in all chondrites, and are called Chondrules. Note the numerous round grains in this Chondrite. Question 2: Based on your chosen texture type, would it be a Sedimentary, Igneous, or Metamorphic rock? Question 1: Based on your computer observations of Igneous and Sedimentary Rock thin sections, would you call the texture of this chondrite Clastic or Crystalline? ![]() A useful byproduct of this low temperature history is that the grains that originally coalesced to make this meteorite 4.5 billion years ago are preserved, as is its original accretionary texture. They all contain some amount of carbon (either as Graphite, or in Organic compounds), which means they have not experienced temperatures much greater than about 300K (about 28¡C, not much warmer than a Spring day in Florida). Carbonaceous Chondrites are the most primordial of all meteorites. The above photomicrographs (Left side in Plain Light right under Crossed Polars) come from a CM3 (Mighei-type) Carbonaceous Chondrite. What we're going to do now is tour through some pictures of meteorite textures and makeup as seen through a petrographic microscope, to see what kinds of unique features they have. When looked at through a microscope, Meteorites show many of the same features as rocks from the Earth, except that the stuff they are made of is very different. Meteorites Under a Microscope: A Web Tour and Exercise! ![]()
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |