Natural Resources Building - East Entrance Exterior

East door Natural Resources BuildingSteps and platform The stone is a light gray, medium-grained granite composed of translucent white feldspar crystals (65-80%), light gray glassy quartz grains (15-20%), and black biotite mica crystals (5-10%). Supplied by the Cold Springs Granite Company of Cold Springs, Minnesota, the rock is probably from the Warman area, Kanabec County, in east-central Minnesota. An igneous rock, the granite formed from molten magma that cooled deep underground during the Precambrian Era, more than a billion years ago.

Limestone balls and exterior trim The pair of large balls on the platform in front of the building and the exterior trim (cornices, string course, lintels, sills, entry posts) consist of light gray limestone mottled with whole fossils, fossil fragments, and pellets - all cemented together by calcite, a common rock-forming mineral composed of calcium carbonate.

Closer inspection of the limestone reveals sediment layering called bedding. Each layer of shelly and pelletal debris was deposited on the floor of a warm, shallow sea and often reworked by wave and tidal currents. High-energy, or fast-moving, waves deposited layers of coarse grained fossil fragments and low-energy, or slow-moving, waves deposited layers of finer grained fragments.

limestone ballAs time passed, these layers were buried deeper and deeper, finally becoming compacted and cemented into limestone, a sedimentary rock. The rock unit that supplied this stone, the Salem Limestone, accumulated in seas that covered what is now the Midwest during the Mississippian Period, between about 360 and 320 million years ago. 

The Salem Limestone came from a Bloomington Limestone Company quarry near Bloomington in south-central Indiana. Extensively quarried between Bloomington and Bedford, Indiana, it is marketed under the trade names Indiana Limestone and Bedford Limestone. An excellent building stone due to its durability, attractiveness, and economy, the Salem Limestone has been quarried in Indiana since at least 1827. It is standard construction material in American buildings, particularly in the Midwest. 

NRB door trimExterior door trim The light gray, faintly mottled limestone that frames the door contains whole fossils, fossil fragments, and pellets. It was originally a shell-sand deposit like the Salem Limestone. Unlike the Salem, this limestone is not visibly porous; calcite cement has filled all the spaces between grains. Consequently, it takes a polish.

This stone, called the Ozark Tavernelle Marble, and three others used inside the building, were supplied by the Carthage Marble Corporation of Carthage, southwestern Missouri. The stone industry gives the name Ozark Tavernelle Marble to limestones that take a high polish and to marbles - the white and varicolored metamorphic carbonate rocks used to make gravestones, statues, and buildings. Tavernelle is an old building stone term that means spotted or mottled.

Ozark Tavernelle, cut from a 2- to 3-foot thick bed in Carthage Quarry, is the lowest of the three beds that supplied cut stone for the Natural Resources Building. All three beds are part of the Warsaw Formation of Mississippian age.