Flow lines

Some few meteorites have "flow lines" but some terrestrial rocks, both natural and man-made, have flow features

Northwest Africa 2998 is an “oriented” meteorite. It came through the atmosphere without tumbling front to back. Melt formed on the leading edge and flowed toward the trailing edge during its entire entry. Oriented meteorites frequently have a rounded, conical (“nose cone”) leading edge. Fusion crust covers the whole meteorite, however, except where it has chipped off since landing on Earth. Feldspathic lunar meteorites like NWA 2998 have lighter-colored fusion crusts than do ordinary chondrites, but where it has chipped off, the interior is even lighter colored. This characteristic is typical of nearly all meteorites and is one of the reasons I say below that none of the rocks in the mosaic has a fusion crust.

Many people have told me that they think their rock is a meteorite because it has “flow lines.” Few meteorites have flow lines.

Flow lines and other flow-like features are common on meteorwrongs, however. The photos below were all sent to me by persons who inquired whether the object was a meteorite because it had “flow lines.” Note that none of the objects has a fusion crust. Note also that meteorite flow lines are external features – they only occur in the fusion crust on the outer 1-2 mm of the rock . It is clear in some of the photos that the lines are a reflection the internal crystalline structure of the rock, not a surface feature.

This is simple: If a rock does not have a fusion crust, then it does not, and cannot, have meteorite flow lines.

Note that none of these apparent flow features is on a “nose cone;” they are on flat parts. Most of these things are industrial slag – once molten stuff that was so viscous that flow features froze as the liquid cooled. Flow features do occur on terrestrial basalts, however. For reasons I do not understand, some hematite concretions have flow-like features, although they were never molten.