Why this rock is probably not a meteorite:

1) They have rough exteriors. The smooth coating on the rock on the upper left is not a fusion crust but the chill skin or crust that forms where molten lava is exposed to air. Note that it is flat (top surface of lava flow). It does not surround the rock, like a fusion crust.

2) They're full of holes. Stony meteorites aren't full of holes.   
  
What are they?

These rocks are vesicular basalts, which are very common in the western U.S. and Hawaii. See meteorwrongs 16 and 18. These rocks were found under a tree in someone's yard. It is quite likely that they had been put there by someone else for landscaping purposes.

Note added later: A reader of this page suggested an alternate explanation, that these are fulgurites - "rocks" formed from a lightning strike on the tree near where they were found.
    
The finder of these rocks noticed that they look a lot like lunar meteorite QUE 94281. They do superficially, but not in detail. QUE94 is a fragment broken from a larger stone, so it has some rough edges, like the rocks above. The fusion crust on QUE94 coats only part of the stone. However, the interior of QUE94 does not contain gas bubbles (although that's hard to see in the photos) because it was never molten like the basalts pictured here. Like many lunar meteorites, QUE94 is a regolith breccia - lunar soil that was shock compacted into a hard rock by the impact of a meteoroid on the Moon. Before it was shock compacted, the fine-grained material had soaked up a lot of solar wind at the surface of the Moon. The solar wind is mostly hydrogen and helium, both gases. Ions of these gases were implanted into the fine-grained lunar "soil." The fusion crust of QUE94 and several other lunar meteorites is vesicular because the solar-wind-implanted gases escape when the exterior melts as the meteoroid passes through Earth's atmosphere at high speed. So, a lunar regolith breccia is vesicular on the outside but not vesicular on the inside - just the opposite of these rocks. (Actually, in the chill skin of the rock on the upper right, some just-broken gas bubbles were frozen, leaving depressions and a few holes.) Finally, QUE 94281 is a breccia - a rock made up of bits and pieces of other rocks. Most of the rock fragments making up QUE94 are, in fact, pieces of basalt, like the rocks above. However, QUE94 also contains fragments of rocks from the lunar highlands. These clasts (anorthosites) are light-colored; a few can be seen in the photos of our QUE 94281 web page.

One other thing to notice: In many terrestrial basalts (like meteorwrong number 16), the vesicles are elongated. This happens in two ways. (1) Cooling lavas are often very viscous, so even in a ponded magma the gas bubbles get stretched out as they rise to the surface. (2) If lava is flowing down the side of a volcano, the gas bubbles also get stretched out from flow in a viscous magma. The rocks above have stretched and irregularly shaped vesicles probably from flow. Because of the composition of lunar basalts (high iron and virtually no water), lunar basaltic magmas were of very low viscosity - they flowed like water. That's why there are no big conical volcanoes on the Moon. So, in lunar basalts, vesicles are mostly round because of the combination of low gravity (if there is no gravity, bubbles don't rise) and low-viscosity magmas. (See "vesicles & amygdules" for some photos of vesicular lunar basalts.) Round vesicles occur in some terrestrial basalts when the viscosity of the magma is low and the magma is not moving very fast.



www.catchafallingstar.com
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