METEORITE OR METEORWRONG?

vesicles in meteorites - basalts

As mentioned here, vesicles only develop in rocks that cool from a liquid. Most meteorites come from asteroids, and almost all asteroids are too small to have volcanoes, thus very few meteorites are igneous rocks, that is, rocks that formed from cooling of a liquid (lava). Most such rocks among the meteorites are basalts. Among meteorites, the only igneous rocks are the eucrites and diogenites (believed to come from a large asteroid like Vesta that had volcanoes), most of the martian meteorites (Mars has some really big volcanoes), and some lunar meteorites. So far, there have been no vesicular martian or lunar basaltic meteorites discovered. A few eucrites and diogenites are moderately vesicular, however.

On the left is a slice of the eucrite Ibitira (width: probably ~10 cm) and on the right is a slice of the diogenite Dhofar 700. These two meteorites are the most vesicular meteorites of which the author is aware. Among all known meteorites, only 1.36% are eucrites and 0.54% are diogenites. Most eucrites and diogenites are not vesicular. Photo courtesy of Ray Stanford. Click on image for enlargement.
Two vesicular lunar basalts, sample 15556 from the Apollo 15 mission (left, cube is 1 inch) and sample 71155 from the Apollo 17 mission (cube is 1 cm). Note that the vesicles are round, not elongated. This occurs because lunar basaltic magmas had very low viscosity and lunar gravity is low. It is possible that some day someone will find a vesicular basaltic lunar meteorite. Click on image for enlargement.

vesicles in meteorites - impact melts

When two asteroids collide, melting may occur and gas may be released. Sometimes the impact melt traps gas bubbles when it cools. This is a special kind of igneous meteorite, one even rarer than meteorites of volcanic origin.

A few lunar meteorites have vesicles that formed by impact of asteroidal meteorites on the Moon. A spectacular example is Shişr 166.

This is a sawn slice of lunar meteorite Shişr 166. The gray portions are veins of solidified impact melt. Several vesicles occur in the impact melt. A few of the vesicles are filled with calcite (the whitest material) that precipitated from aqueous fluids after the meteorite landed in Oman. Such features are called amygdules.

 

Another vesicular lunar meteorite are the four paired stones of Dhofar 081/280/910/1224. These stones have vesicles in the glassy matrix because the matrix was once molten and probably consisted of melted regolith that contained solar wind gases. It's probably more accurate to call these cavities vugs, not vesicles, because most are not spherical.

Slices of lunar meteorite Dhofar 910, each about 1 cm across. Notice that the clasts do not have vesicles or vugs but the once-glassy (now devitrified) matrix does. Again, the voids are all less than a millimeter in size. Photos courtesy of Haberer-Meteorites.

Keep in mind, however, that meteorites are very rare and lunar meteorites are exceedingly rare - less than 1 in 1000 meteorites are from the Moon.

Bottom line: If you have a vesicular rock, it's probably not a meteorite. Such rocks are very common on Earth but are exceedingly rare among meteorites.

vesicles and amygdules

vesicles in meteorite fusion crusts


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www.catchafallingstar.com


Prepared by:

Randy L. Korotev


Department of Earth and Planetary Sciences
Washington University in St. Louis


Please don't contact me about the meteorite you think you’ve found until you read this and this.

e-mailkorotev@wustl.edu