Natural Resources Building - East Entrance Interior

Floor and stairs The brown to dark brown limestone that contains very light brown speckles is Nerobi Marble. It came from a bed in the Warsaw Formation at Carthage quarry. Nerobi Marble occurs above the Ozark Tavernelle and Ozark Veined beds. The speckles in the rock are round, donut-shaped crinoid columnals, the skeletal part of animals related to starfish and ancestors of the present day crinoids. Like other limestones used in the Natural Resources Building, the Nerobi Marble formed in a warm, shallow sea. It was originally calcium carbonate sand largely composed of animal plates and columnals, and it was deposited by sea currents strong enough to sort the grains by size and wash away most of the fine grained chalky muds that were present.

close-up of pillar Lower wall veneer, pillar, and baseboard The dark grayish brown stone with the streaks of light grayish brown mottles is Dark Plattin Marble. This Ordovician-age stone, supplied by Carthage Marble Company, was probably extracted from a quarry near Batesville in north-central Arkansas. The geologic name of the stone is the Plattin Limestone. It is about 455 to 460 million years old. 

The rock was originally deposited in layers consisting mostly of very fine grained calcite mud and a little bit of clay. It was deposited in a shallow sea, or possibly in a tidal estuary where marine animals thrived and some soil was washed into the ocean from the land. The stone shows cross sections of thin wafer-like brachiopods and a few coral colonies - animals that lived in soft mud. Many of the light brown mottles appear to be sections of mud-filled animal burrows.

This limestone was cut at right angles to the bedding to show the various bedding colors and accentuate the mottled effect. The burrows and other large pores were filled with mud from the bottom upward, and where the top of a pore was not filled, glassy gray calcite crystals grew in the space. These calcite fillings ("birds-eyes") indicate which way was "up" when the sediments were originally deposited.

Hall, walls, door frames The blocks of mottled, light yellowish gray stone are cut from dolomite, a rock native to Illinois. It was quarried and finished in Joliet by the Adam Groth Stone Company. In that area the dolomite was called Joliet Marble. A few miles north, near Lemont, which was once known as Athens, the same dolomite was called Athens Marble. The stone comes from the Sugar Run Formation of Silurian age (438 to 408 million years old).

wall trim Beds of the Sugar Run Formation in the Joliet-Lemont region have furnished more building stone than any other rock unit in the state. Dolomite was a very popular stone in the late 19th century to the early 20th century. The stone was generally used to face exterior walls because weathering turns it a distinctive pale yellow. It is found in older public and private buildings throughout the state but particularly in the northeast. Chicago's Water Tower is among the best known examples.

This dolomite is a sedimentary rock that was originally deposited as a fine grained calcite mud. From time to time, a little mud (clay and silt) from the land was added to the sediment. The mud forms the darker gray streaks and mottles in the stone. At some point, probably not long after deposition, water carried magnesium into the calcium carbonate (calcite) mud and changed it to calcium- magnesium carbonate (dolomite) by replacing some of the calcium with magnesium.

Because the crystal structure of dolomite is more compact than that of calcite, the process of replacing calcite with dolomite causes a decrease in volume and a corresponding increase in porosity in the dolomite. The process frequently obliterates the distinctive shapes and internal structure of fossils. Consequently, few, if any, animal skeletons or hard parts are visible in the dolomite, although there are traces of burrowing animals. 

The streaks of sooty black, rust-spotted pyrite (an iron sulfide mineral) probably formed in fecal matter. Rusty specks of pyrite are very noticeable on the east pillar of the east entrance. Burrowing animals probably disturbed what were originally continuous bedding surfaces and produced the wavy, broken surfaces visible on the ends of some blocks.

wall with figureThe stone has a honed finish; it has been ground smooth but not polished. The gray marbling is produced by cutting the exposed face parallel to the plane of the rock's bedding so that the gray mud films, or laminae, are intersected.

Rest room partitions and wall veneer These polished limestone panels are Ozark Veined Marble from the Carthage Marble Corporation Quarry in Missouri. The light gray and light olive gray limestone contains wispy, dark gray figures. It comes from the same quarry ledge as the Ozark Tavernelle stone. The veined rock comprises about the upper three-fourths of the ledge and the Tavernelle the lower one-fourth. The veins in the stone are stylolites.

These limestone panels are cut parallel to the bedding and perpendicular to the stylolite seams. The dark gray, wispy figures occur where the cutintersects the top of the stylolites. Stylolites can also by seen in the lower wall veneer, pillars, and baseboard in the east entrance foyer.

The limestone is part of the Warsaw Formation of Mississippian age. Patches of horn corals and brachiopods are visible in the panels as dark gray skeletal sections. These fossils are the remains of animal communities that lived on the bottom of a Mississippian sea that existed from 360 to 320 million years ago.