Listwanite (also sometimes spelled ''listvenite'', ''listvanite'', or ''listwaenite'') is a rock type that forms when the groundmass of

ultramafic Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed ...

rocks, most commonly mantle peridotites, is partially altered to carbonate minerals and cut by ubiquitous carbonate veins containing one or more of magnesite, calcite,

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

, ankerite, and/or

siderite Siderite is a mineral composed of iron(II) carbonate (FeCO3). It takes its name from the Greek word σίδηρος ''sideros,'' "iron". It is a valuable iron mineral, since it is 48% iron and contains no sulfur or phosphorus. Zinc, magnesium and ...

. Original pyroxene and

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...

in the peridotite are commonly altered to Mg- or Ca-carbonate and hydrous Mg-silicates, such as serpentine and

talc Talc, or talcum, is a clay mineral, composed of hydrated magnesium silicate with the chemical formula Mg3Si4O10(OH)2. Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent a ...

. Complete carbonation of peridotite means that every single atom of magnesium and calcium as well as some of the iron atoms have combined with CO₂ to form secondary carbonate minerals such a magnesite, calcite, and siderite, while the remaining

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...

atoms, formerly found in pyroxene and olivine (prior to alteration), are found in quartz, serpentine, and talc. Thus, in terms of bulk mineralogy, listwanites consist primarily of quartz (often of a rusty red colour), carbonate, serpentine, talc, ± mariposite/fuchsite (i.e., Cr-muscovite) ± gold.

Formation

Geologists are still studying how listwanites form, but they likely form through the reaction of CO₂-rich fluids with peridotites at approximately 50 to 200 °C. Faults and fractures permit the percolation of the CO₂-rich fluids through peridotite, so the formation of listwanites is generally considered to be structurally controlled.

CO2 content

Listwanites are important rocks to study for a number of reasons. First of all, listwanites contain large amounts of CO₂ which originated from fluids that is now stored in solid mineral form. Recently, geologists and other scientists have been investigating the potential of storing CO₂ in solid minerals (which are more stable than CO₂ stored as a liquid or gas) through carbonation of mafic and ultramafic rocks.

Mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks incl ...

and ultramafic rocks take up significant CO₂ through their natural alteration processes. However, the natural carbonation rates of these rocks are too slow to significantly offset anthropogenic CO₂ emissions. Therefore, scientists are currently investigating if it is possible to geoengineer CO₂ uptake in mafic and ultramafic rocks so that this CO₂ uptake happens more quickly. This could be done, perhaps, by fracturing and heating and injection of CO₂-rich fluids. This is already being tested in mafic basalts through the CarbFix Project in Iceland and ultramafic peridotite through 44.01 Project in the

Semail Ophiolite The Samail Ophiolite (also spelled Semail Ophiolite) of the Hajar Mountains of Oman and the United Arab Emirates is a large slab of oceanic crust, made of volcanic rocks and ultramafic rocks from the Earth's upper mantle, that was overthrust ont ...

of Oman. In addition to the recent interest in listwanites for

carbon sequestration Carbon sequestration is the process of storing carbon in a carbon pool. Carbon dioxide () is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in lan ...

efforts, listwanites are also important because they are often associated with economic mineral deposits, particularly gold deposits.

References

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Formation

CO2 content

References

See also