Uranium ore support a neutron-mediated chain reaction). Uranium, thorium, and potassium are the main elements contributing to natural terrestrial radioactivity. Uranium has the highest atomic weight of the naturally occurring elements and is approximately 70% denser than lead, but not as dense as tungsten, gold, platinum, iridium, or osmium. It is always found combined with other elements. Along with all elements having atomic weights higher than that of iron, it is only naturally formed in supernova explosions. The primary uranium ore mineral is uraninite (UO) (previously known as pitchblende). A range of other uranium minerals can be found in various deposits. These
Galena Historic District Places. The Galena Historic District contains more than 1,000 buildings constructed before 1900 that are considered contributing properties. The center of downtown Galena is laid out in three parallel segmental tiers starting at Main Street closest to the river. Beyond Main Street, and at a higher elevation, are Bench and Prospect Streets. Main Street forms the primary commercial strip through Galena and is lined with buildings two, three, and four stories tall. Most of Main Street's structures are built of red brick and cast in Federal style of the simple commercial style of the 1840s. On Bench Street, most of