Wendy Cropf, age 14, of Lititz, Pa., for her question:
HOW CAN YOU TELL WHEN YOU FIND A METEORITE?
A fallen meteorite once whizzed through the solar system maybe for billions of years. When it struck the earth, it became grounded forever. Finding it is very exciting, for you then own a genuine traveler from outer space. What’s more, if it happens to be a special meteorite called a tektite, it may be a genuine moon rock.
When a meteorite lies on the ground for a long time, it may become disguised as an ordinary earth pebble. This is because the weather tends to wear away its telltale crusty surface. Actually it is made from ordinary minerals which are common in the earth. True, their crystal formation is somewhat different, but it usually takes an expert to detect them.
For the average rock hound, the obvious clue is the meteorite’s dark, glassy crust. This was formed as it plummeted down through the atmosphere, turning its speed energy into heat energy. It became so hot that its glowing surface melted and formed that glassy crust. Gases within bubbled out, adding pits and bumps. Chances are, the rush through the air also molded the whole thing into a rough cone shape.
If an odd shaped pebble looks like it has been bashed around in a furnace, chances are it is a meteorite. It may be a metallic meteorite, made mostly of iron with traces of nickel. In this case, the inside under the crust is silvery gray. When sliced, polished and seen under a microscope, its crystalline formation reveals a neat network of streaks in a pattern of diamonds and letter Xs.
It may be a stony meteorite made from silicates and several of 30 other common earth minerals. Its dark, glassy crust tends to be more bumpy and less pitted. Its interior is usually grayish, stony material arranged in unusual granule formations. Often its stony minerals are mixed with specks of iron.
Certain meteorites are made from soft clays and crumbly charcoals. Usually they shatter on impact and are decomposed by the weather. So the meteorites we find are most likely to be either the metallic or the stony types. Both have dark, glassy crusts with bumps or pits or both.
Most of the fallen meteorites are pebble size. But some are as big as boulders, weighing a ton. Usually the large stony types shatter on impact. The large metallic types are more likely to survive—and some of these monsters weigh as much as 70 tons.