( 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 . 11 meteor tweets we wish we 'd thought of . 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 . Russia starts cleanup after meteor strike . 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 . Opinion : Meteor shows why it is crucial to keep an eye on the sky . 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 . Opinion : A meteor and asteroid : 1 in 100 million odds . 5 things to know about meteors and asteroids . 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 .
NEW : Black market for claimed meteorites emerges in Russia , state media report . Scientists found some small fragments on frozen Lake Chebarkul . A larger fragment may be under the frozen surface of the lake , scientists say . The explosion Friday damaged thousands of buildings and injured 1,000 people .