Ilsemannite is an uncommon

amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal. Etymology The term comes from the Greek ''a'' ("wi ...

complex heterovalent

molybdenum oxide Molybdenum oxide may refer to: * Molybdenum(IV) oxide (molybdenum dioxide, ) * Molybdenum(VI) oxide Molybdenum trioxide describes a family of inorganic compounds with the formula MoO3(H2O)n where n = 0, 1, 2. These compounds are produced on th ...

, that was first published in 1871, and has been a valid species since pre- IMA. It is a grandfathered mineral, meaning the name ilsemannite is still believed to refer to a valid species. However, it is likely that specimens formed under different conditions, in different localities do not have the same composition, and may even be a mixture of compounds. Furthermore, it is hard to analyze the specimens due to them being a mixture, hence why adequate analyses are lacking of said mineral. Ilsemannite is believed to be identical to synthetic molybdic oxide.

Properties

Ilsemannite is soluble in water, which at first produces a greenish blue color, which later changes to a deep molybdenum-blue. This is probably why Native Americans believed that ilsemannite colored the waters blue in the

Idaho Springs The City of Idaho Springs is the Statutory City that is the most populous municipality in Clear Creek County, Colorado, United States. Idaho Springs is a part of the Denver–Aurora–Lakewood, CO Metropolitan Statistical Area. As of the 2010 ...

area, however, this has been debunked. Ilsemannite is now believed to consist of molybdenum (66.34%) and oxygen (33.19%), having a negligible amount of hydrogen (0.46%) in it. It has an earthy, dull, clay-like texture, and it is amorphous, meaning ilsemannite does not grow crystals. It does not show any radioactive properties. In an occurrence near

Ouray, Utah Ouray is an unincorporated village of the Uintah and Ouray Indian Reservation, located in west‑central Uintah County, Utah, United States. Description The community is located primarily on the north bank of the confluence of the Duchesne and ...

, researchers found ilsemannite specimens disseminated through a rock. Analyses showed that about 10% of the sample was water-soluble, and that the water-soluble portion contains

iron sulfate Iron sulfate may refer to: * Ferrous sulfate, Iron(II) sulfate Iron(II) sulfate (British English: iron(II) sulphate) or ferrous sulfate denotes a range of salts with the formula Fe SO4·''x''H2O. These compounds exist most commonly as the hept ...

. Back then, in 1917, researches concluded that specimens from other localities all showed that iron sulfate was present in each of them, which is why the formula of said mineral was believed to be MoO₃·SO₃·5H₂O. A specimen from

Saxony Saxony (german: Sachsen ; Upper Saxon: ''Saggsn''; hsb, Sakska), officially the Free State of Saxony (german: Freistaat Sachsen, links=no ; Upper Saxon: ''Freischdaad Saggsn''; hsb, Swobodny stat Sakska, links=no), is a landlocked state of ...

mixed with iron sulfate showed only small amounts of iron, and gave a strong sulfate reaction. Another specimen from

Carinthia Carinthia (german: Kärnten ; sl, Koroška ) is the southernmost States of Austria, Austrian state, in the Eastern Alps, and is noted for its mountains and lakes. The main language is German language, German. Its regional dialects belong to t ...

had the same reaction, however this specimen had only a trace of

ferric iron In chemistry, iron(III) refers to the element iron in its +3 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe3+. The adjective ferric or the prefix ferri- is often used to s ...

, with no

ferrous iron In chemistry, iron(II) refers to the element iron in its +2 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe2+. The adjective ferrous or the prefix ferro- is often used to spe ...

in it. The specimen from

Cripple Creek, Colorado Cripple Creek is a statutory city that is the county seat of Teller County, Colorado, United States. The city population was 1,155 at the 2020 United States Census. Cripple Creek is a former gold mining camp located southwest of Colorado Sprin ...

showed the exact same reaction. During a study, it was found out that jordisite alters to ilsemannite more readily than it does to

molybdenite Molybdenite is a mineral of molybdenum disulfide, Mo S2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure. The atomic structure consists of a sheet of molybdenum ato ...

, probably due to its amorphous state. This, among the scarcity of jordisite in mineral deposits, could explain why ilsemannite can be discovered in molybdenum districts. When first found, the mineral is usually black-blue or black in color, and it turns to blue-green and fades when exposed to sunlight. When put in a furnace alongside

cinnabar Cinnabar (), or cinnabarite (), from the grc, κιννάβαρι (), is the bright scarlet to brick-red form of Mercury sulfide, mercury(II) sulfide (HgS). It is the most common source ore for refining mercury (element), elemental mercury and ...

, the

calcined Calcination refers to thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), genera ...

product's color changed to a purplish pink color. Chemical analyses of the material were not obtained due to the fact that the very thin coating surrounding ilsemannite couldn't be separated from the specimens. Underneath this coating there was a black, submetallic, sectile mineral first believed to be

metacinnabar Metacinnabar is the cubic form of mercury sulfide (HgS). It is the high temperature form and trimorphous with cinnabar (trigonal structure) and the higher temperature hypercinnabar (hexagonal structure). It occurs with cinnabar in mercury depos ...

, but it was later proved to be a molybdenum compound. It was obvious that ilsemannite was an alteration product of this compound. The specimen from Colorado was described to have this coating as well, only that this time it was green. It is believed that the specimen was actually either a yellow iron sulfate, or a yellow

molybdite Molybdite is the naturally occurring mineral form of molybdenum trioxide MoO3. It occurs as yellow to greenish needles and crystallizes in the orthorhombic crystal system. Discovery and occurrence Molybdite was first described in 1854 for and o ...

, which was colored green due to the ilsemannite solution.

Occurrences and localities

Ilsemannite forms by the oxidation of molybdenum-bearing minerals, making it a

secondary mineral A primary mineral is any mineral formed during the original crystallization of the host igneous primary rock and includes the essential mineral(s) used to classify the rock along with any accessory minerals. In ore deposit geology, hypogene processe ...

. It is associated with

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywall. ...

wulfenite Wulfenite is a lead molybdate mineral with the formula Pb Mo O4. It can be most often found as thin tabular crystals with a bright orange-red to yellow-orange color, sometimes brown, although the color can be highly variable. In its yellow form ...

melanterite Melanterite is a mineral form of hydrous iron(II) sulfate: FeSO4·7H2O. It is the iron analogue of the copper sulfate chalcanthite. It alters to siderotil by loss of water. It is a secondary sulfate mineral which forms from the oxidation of prima ...

halotrichite Halotrichite, also known as ''feather alum'', is a highly hydrated sulfate of aluminium and iron. Its chemical formula is FeAl2(SO4)4·22H2O. It forms fibrous monoclinic crystals. The crystals are water-soluble. It is formed by the weathering and ...

, molybdenite, jordisite, and other oxidized uranium minerals; however, it had been found in association with

as well in 1939. In the aforementioned encounter, ilsemannite was found as veinlets and as irregular lenses or pods in association of the cinnabar specimens. These specimens were described to often stain the nearby

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

s a light blue color. It has a type locality of Carinthia, and although it is an uncommon mineral, it has been described in more than a dozen of other localities since then. Despite this fact, there is still an uncertainty lingering around the chemical composition and the origin of the mineral.

References

{{Commons category-inline Mineral County, Colorado Amorphous solids Molybdenum minerals