Limonite in the context of Pisolite

Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the form of magnetite (Fe
₃O
₄, 72.4% Fe), hematite (Fe
₂O
₃, 69.9% Fe), goethite (FeO(OH), 62.9% Fe), limonite (FeO(OH)·n(H₂O), 55% Fe), or siderite (FeCO₃, 48.2% Fe).

Ores containing very high quantities of hematite or magnetite (typically greater than about 60% iron) are known as natural ore or [direct shipping ore], and can be fed directly into iron-making blast furnaces. Iron ore is the raw material used to make pig iron, which is one of the primary raw materials to make steel — 98% of the mined iron ore is used to make steel. In 2011 the Financial Times quoted Christopher LaFemina, mining analyst at Barclays Capital, saying that iron ore is "more integral to the global economy than any other commodity, except perhaps oil".

Ironstone is a sedimentary rock, either deposited directly as a ferruginous sediment or created by chemical replacement, that contains a substantial proportion of an iron ore compound from which iron (Fe) can be smelted commercially.

Not to be confused with native or telluric iron, which is very rare and found in metallic form, the term ironstone is customarily restricted to hard, coarsely banded, non-banded, and non-cherty sedimentary rocks of post-Precambrian age. The Precambrian deposits, which have a different origin, are generally known as banded iron formations. The iron minerals comprising ironstones can consist either of oxides, i.e. limonite, hematite, and magnetite; carbonates, i.e. siderite; silicates, i.e. chamosite; or some combination of these minerals.

Opal is a hydrated amorphous form of silica (SiO₂·nH₂O); its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Due to the amorphous (chemical) physical structure, it is classified as a mineraloid, unlike crystalline forms of silica, which are considered minerals. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt.

The name opal is believed to be derived from the Sanskrit word upala (उपल), which means 'jewel', and later the Greek derivative opállios (ὀπάλλιος).

Anglesite is a lead sulfate mineral with the chemical formula PbSO₄. It occurs as an oxidation product of primary lead sulfide ore, galena. Anglesite occurs as prismatic orthorhombic crystals and earthy masses, and is isomorphous with barite and celestine. It contains 74% of lead by mass and therefore has a high specific gravity of 6.3. Anglesite's color is white or gray with pale yellow streaks. It may be dark gray if impure.

It was first recognized as a mineral species by William Withering in 1783, who discovered it in the Parys copper-mine in Anglesey; the name anglesite, from this locality, was given by F. S. Beudant in 1832. The crystals from Anglesey, which were formerly found abundantly on a matrix of dull limonite, are small in size and simple in form, being usually bounded by four faces of a prism and four faces of a dome; they are brownish-yellow in colour owing to a stain of limonite. Crystals from some other localities, notably from Monteponi [it] in Sardinia, are transparent and colourless, possessed of a brilliant adamantine lustre, and usually modified by numerous bright faces. The variety of combinations and habits presented by the crystals is very extensive, nearly two hundred distinct forms being figured by V. von Lang in his monograph of the species; without measurement of the angles the crystals are frequently difficult to decipher. There are distinct cleavages parallel to the faces of the prism (110) and the basal plane (001), but these are not so well developed as in the isomorphous minerals barite and celestite.

Felsite is a very fine-grained volcanic rock that may or may not contain larger crystals. Felsite is a field term for a light-colored rock that typically requires petrographic examination or chemical analysis for more precise definition. Color is generally white through light gray, or red to tan and may include any color except dark gray, green or black (the colors of trap rock). The mass of the rock consists of a fine-grained matrix of felsic materials, particularly quartz, plagioclase and potassium feldspar, and may be termed a quartz felsite or quartz porphyry if the quartz phenocrysts are present. This rock is typically of extrusive origin, formed by compaction of fine volcanic ash, and may be found in association with obsidian and rhyolite. In some cases, it is sufficiently fine-grained for use in making stone tools. Its fine texture and felsic components allow for good knapped pieces, much like working chert, producing conchoidal fracture.

Dendritic manganese oxides such as pyrolusite or iron oxides such as limonite may precipitate along rock crevices, giving some rock chunk surfaces multicolored or arborescent patterned textures.

A pisolite (from Ancient Greek πίσον (píson) 'pea') is a sedimentary rock made of pisoids, which are concretionary grains – typically of calcium carbonate which resemble ooids, but are more than 2 mm in diameter. These grains are approximately spherical and have concentric layers reaching 10 mm in diameter.

Bauxites, limonites, and siderites often have a pisolitic structure.

Pelagic red clay, also known as simply red clay, brown clay or pelagic clay, is a type of pelagic sediment.

Pelagic clay accumulates in the deepest and most remote areas of the ocean. It covers 38% of the ocean floor and accumulates more slowly than any other sediment type, at only 0.1–0.5 cm/1000 yr. Containing less than 30% biogenic material, it consists of sediment that remains after the dissolution of both calcareous and siliceous biogenic particles while they settled through the water column. These sediments consist of eolian quartz, clay minerals, volcanic ash, subordinate residue of siliceous microfossils, and authigenic minerals such as zeolites, limonite and manganese oxides. The bulk of red clay consists of eolian dust. Accessory constituents found in red clay include meteorite dust, fish bones and teeth, whale ear bones, and manganese micro-nodules.

Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the form of magnetite (Fe
₃O
₄, 72.4% Fe), hematite (Fe
₂O
₃, 69.9% Fe), goethite (FeO(OH), 62.9% Fe), limonite (FeO(OH)·n(H₂O), 55% Fe), or siderite (FeCO₃, 48.2% Fe).

Ores containing very high quantities of hematite or magnetite (typically greater than about 60% iron) are known as natural ore or direct shipping ore, and can be fed directly into iron-making blast furnaces. Iron ore is the raw material used to make pig iron, which is one of the primary raw materials to make steel — 98% of the mined iron ore is used to make steel. In 2011 the Financial Times quoted Christopher LaFemina, mining analyst at Barclays Capital, saying that iron ore is "more integral to the global economy than any other commodity, except perhaps oil".

Fire agate is a variety of chalcedony that displays fire-like iridescent flashes. It is found only in certain areas of central and northern Mexico and the southwestern United States (New Mexico, Arizona and California). Despite its name, it is not a true agate, since it typically does not have bands. Approximately 24-36 million years ago, during the Tertiary Period, these areas were subjected to massive volcanic activity. Fire agates were formed when hot water, saturated with silica and iron oxide, filled cracks and cavities in the surrounding rock and solidified into chalcedony layered with crystallized iron oxide.

Fire agates have beautiful iridescent rainbow colors, similar to opal. They have a hardness of 6.5-7 on the Mohs scale, which reduces the occurrence of scratching when polished gemstones are set in jewelry. The vibrant iridescent rainbow colors found within fire agates are created by the Schiller effect, which is also found in mother-of-pearl. The brown color and iridescence of fire agates is due to inclusions of the iron oxides goethite or limonite.