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In geology and particularly in sedimentology, a nodule is a small, irregularly rounded knot, mass, or lump of a mineral or mineral aggregate that typically has a contrasting composition from the enclosing sediment or sedimentary rock. Examples include pyrite nodules in coal, a chert nodule in limestone, or a phosphorite nodule in marine shale.
Chert varies greatly in color, from white to black, but is most often found as gray, brown, grayish brown and light green to rusty red [9] [10] and occasionally as dark green. [11] Its color is an expression of trace elements present in the rock. Both red and green are most often related to traces of iron in its oxidized and reduced forms ...
[34] [35] Septarian nodules are characteristically found in carbonate-rich mudrock. They typically show an internal structure of polyhedral blocks (the matrix) separated by mineral-filled radiating cracks (the septaria) which taper towards the rim of the concretion. The radiating cracks sometimes intersect a second set of concentric cracks.
Flint occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones. [3] [4] Inside the nodule, flint is usually dark grey or black, green, white, or brown in colour, and has a glassy or waxy appearance. A thin, oxidised layer on the outside of the nodules is usually different in colour, typically white and rough in ...
The Corriganville Limestone was first described by J. W. Head in 1972 as part of the Helderberg Group in Allegany County, Maryland, as a gray limestone with chert. [11] C. R. Wood first mapped it as part of the Old Port Formation in Pennsylvania. [12] The type locality is a railroad cut 0.3 mi southeast of Corriganville, Alleghany County ...
“Unabsorbed iron can form complexes with compounds in your gastrointestinal tract that can lead to black stools,” says Samuel A. Akinyeye, M.D., assistant professor in the division of ...
Melena is a form of blood in stool which refers to the dark black, tarry feces that are commonly associated with upper gastrointestinal bleeding. [1] The black color and characteristic strong odor are caused by hemoglobin in the blood being altered by digestive enzymes and intestinal bacteria. [2]
The notched version was probably hafted as a spade. Another advantageous property of the Mill Creek chert was the large size of the nodules, which meant that the corresponding tools could be large. Some hoes were up to 60 centimetres (24 in) in length. [4] The other main use for the chert was large ceremonial bifaces, spatulate celts and stone ...