By Alla Eshchenko and Michael Pearson
(CNN) -- What was in that meteor that exploded spectacularly over Russia's Urals region last week? Radioactive spores? Tiny Martians? Kryptonite?
Nope, just rock and a bit of iron, according to Russian scientists who tracked fragments of the meteor to the frozen surface of Lake Chebarkul.
Scientists from Urals Federal University found 53 small meteorites on the surface of the lake and believe a larger fragment is under water, said Viktor Grokhovsky, the scientist who led the effort.
The fragments point to a rocky meteor with about 10% iron mixed in, Grokhovsky told CNN.
The meteor exploded Friday in the air near Chelyabinsk, leaving behind nothing but meteorites, thousands of broken windows and some pretty spectacular video of it streaking across the sky before exploding in a noisy, luminous fireball.
The explosion startled residents going about their morning business and damaged more than 4,700 buildings, mostly apartments. About 3,500 had been repaired as of Monday, the state-run RIA Novosti news service reported.
About 1,000 people suffered injuries, mostly from flying glass. One woman was flown to Moscow for treatment of a spinal injury, state media reported.
State officials said 19 people remained hospitalized Monday, RIA Novosti reported.
Local officials have estimated the damage at more than 1 billion rubles ($33.2 million), RIA Novosti said. The state applied for 500 million rubles in aid from the federal government to help make repairs, the news service reported.
Chelyabinsk Gov. Mikhail Yurevich promised compensation to all those affected, the official Itar-Tass news agency said.
Police are also monitoring online auction sites and social media after reports of people trying to sell what they claim to be meteorites from Friday's explosion, RIA Novosti said. Some of the sellers are asking as much as $4,000 each, state-run RT television reported.
The U.S. space agency, NASA, said the meteor released nearly 500 kilotons of energy, about 33 times more than the nuclear bomb the United States dropped on Hiroshima, Japan, in 1945.
NASA estimated the meteor's diameter at 55 feet (17 meters) and said it was the largest reported since 1908, when a meteor exploded over Tunguska in remote Siberia, destroying 80 million trees over an area of 820 square miles.
"We would expect an event of this magnitude to occur once every 100 years on average," Paul Chodas of NASA's Near-Earth Object Program Office at the Jet Propulsion Laboratory said last week.
"When you have a fireball of this size, we would expect a large number of meteorites to reach the surface, and in this case there were probably some large ones."
The event was unrelated to the passage of another, larger asteroid some 17,100 miles from earth on Friday, according to scientists.
CNN's Alla Eshchenko reported from Moscow and Michael Pearson wrote and reported in Atlanta. CNN's Phil Black and Laura Smith-Spark also contributed to this report.
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