A nodule in petrology or mineralogy is an irregular rounded to spherical concretion. Nodules are typically solid replacement bodies of chert or iron oxides formed during diagenesis of a sedimentary rock. Nodules may be hollow as geodes or vugs or filled with crystals and intricate geometric shrinkage patterns as in septarian nodules. Petrology is a field of geology which focuses on the study of rocks and the conditions by which they form. ... Mineralogy is an earth science that involves the chemistry, crystal structure, and physical (including optical) properties of minerals. ... A concretion is a solid mineral inclusion within a rock strata that is oval or spherical in shape. ... Chert Chert is a fine-grained silica-rich cryptocrystalline sedimentary rock that may contain small fossils. ... Iron oxide pigment There are a number of iron oxides: Iron oxides Iron(II) oxide or ferrous oxide (FeO) The black-coloured powder in particular can cause explosions as it readily ignites. ... In geology, diagenesis refers to all the chemical, physical, and biological changes undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration (weathering). ... Two types of sedimentary rock: limey shale overlaid by limestone. ... Geode, halved and polished. ... In the lower left, a spherule, or sphere-shaped grain, can be seen penetrating the interior of a small cavity called a vug. ...

Manganese nodules are rounded accumulations of manganese, iron and other metal oxides that accumulate on the deep ocean floor. Polymetallic nodules, also called manganese nodules, are rock concretions on the sea bottom formed of concentric layers of iron and manganese hydroxides around a core. ... General Name, Symbol, Number manganese, Mn, 25 Chemical series transition metals Group, Period, Block 7, 4, d Appearance silvery metallic Atomic mass 54. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ...

Silicic volcanic rocks also form nodular segregations during cooling and recrystalization of rhyolitic and obsidian flows. Thundereggs are geode like nodules that form in volcanic ash deposits during diagenesis. This article is about volcanoes in geology. ... Rhyolite Rhyolite is an igneous, volcanic (extrusive) rock, of felsic composition, with aphanitic to porphyritic texture. ... Obsidian from Lake County, Oregon Top stone is obsidian, below that is pumice and in lower right hand is rhyolite (light color) Obsidian is a type of naturally occurring glass, produced by volcanoes (igneous origin) when a felsic lava cools rapidly and freezes without sufficient time for crystal growth (see... A thunderegg is a type of rock similar to a geode but formed in a rhyolitic lava flow and found only in areas of volcanic activity. ... Diamond Head, a well-known backdrop to Waikiki in Hawaii, is an ash cone that solidified into tuff Volcanic ash is the term for very fine rock and mineral particles less than 2 mm in diameter that are ejected from a volcanic vent. ...