An Article In Meteorite-Times Magazine
by Matt Morgan of Mile High Meteorites and
Gary Curtiss, Rocky Mountain Meteorite Laboratory
Johnstown, Colorado Diogenite
At 4:20 in the afternoon of July 6, 1924, people were gathering for a funeral service in front of a church near the town of Elwell, two miles west of Johnstown, Colorado. Out of nowhere, a sudden sound, likened to that of an airplane engine, filled the quiet day and interrupted the service. A trail of smoke was emblazoned across the blue sky followed by a series of loud explosions. At ground level, “thuds” and “thumps” were heard and a black stone, falling from the sky, stuck near the doors of the church where the service was being held. Thirty minutes after the service, the church undertaker removed a 15-pound stone from the soil at a depth of 20 inches.
Following the sight and sounds of the fireball, 27 fusion-crusted stones were recovered, with a total weight of 88.9 pounds, the largest weighing 51.8 pounds. Most of the meteorites embedded themselves in the soft soil, however a few landed within feet of farm workers out in their fields. The 51.8-pound stone buried itself 5-feet-deep while 5 miles to the south, a 7-pound stone came to rest on the surface. Like other meteorite falls, the fragments were distributed in an ellipse, however the distribution pattern of the Johnstown meteorites was unusual. Instead of the largest stones falling at the far end of the ellipse, they fell out first, creating an inverted strewn field. The smaller stones rained down on rooftops in the town of Mead, located 10 miles away from the spot where the first stones fell. Local residents reportedly picked up many pea- to walnut-sized stones.
The Johnstown meteorite is classified as a calcium-poor diogenite, being composed mainly of hypersthene, with minor amounts of plagioclase and olivine. The cut and polished surface of a Johnstown meteorite presents a picture of large, green hypersthene crystals set in a creamy-white brecciated matrix. The large size of the hypersthene crystals suggests that Johnstown meteorite cooled slowly, probably within a magma chamber beneath the surface of a differentiated asteroid, like 4 Vesta.
Top 5 institutions containing Johnstown:
1. 37.47 lbs American Museum of Natural History, New York
2. 11.46 lbs Denver Museum of Nature and Science
3. 5.47 lbs Arizona State University, Tempe
4. 3.02 lbs U.S. National Museum, Washington
5. 2.87 lbs Museum of Natural History, London
Hovey, E. O., 1925, A new meteoric stone from Johnstown, Weld County, Colorado: American Museum Novitates, n. 203.
Nininger, H. H., 1952, Out of the sky: Dover Publications, 336 p.
Norton, O. R., 2002, The Cambridge encyclopedia of meteorites: Cambridge University Press, 354 p.
Weir, D., 1997-2002, Description of the Johnstown meteorite, on-line at http://www.geocities.com/~dweir/JOHNSTOW.HTM