Dear Colleagues,

The theme of this Special Issue of Minerals, “Iron Silicide Minerals”, explicitly focuses on its occurrence in nature. In industry, the best known is iron monosilicide FeSi, which is used, among other things, for the production of various alloys.

Iron silicides in nature are very rare, little known, and have only become accessible to science in the last few decades. At the same time, much (origin, formation) is still unclear.

Minerals xifengite, Fe5Si3, and gupeiite, Fe3Si, components of the Yanshan meteorite at the type-locality Chengde, Lever in China, which was published in 1984, got their names from Xifengkou and Gubeikou at passages of the Great Wall of China. Somewhat earlier, in 1960, the natural equivalent of industrial FeSi, naquite, was discovered, but the industrial aspect of their origin remained essential for a long time. Other rare iron silicide minerals include the FeSi2 (linzhite), luobusaite (Fe0.84Si2), and nickel- and titanium-bearing iron silicide minerals suessite (Fe,Ni)3Si and zangboite (TiFeSi2). A special role has been given to the mineral hapkeite Fe2Si, which, based on a 1973 prediction by Prof. Bruce Hapke, was first detected on Earth in 2004 in the lunar meteorite Dhofar 280 and officially recognized as a mineral in the same year.

The reason for the rare occurrence of iron silicide minerals on Earth is the formation conditions, which require extreme temperatures and an extremely reducing environment, which is hardly ever present in terrestrial processes. Accordingly, iron silicides have been detected in some fulgurites, including most recently (2020) in a Michigan fulgurite. Eutectic intergrowth texture of two iron silicides revealed naquite and linzhiite or naquite and xifengite. Iron silicide particles found in Southern Urals, Russia, up to 1 m deep in Pleistocene sediments, were studied as a possible new class of meteorites, but in the end, a terrestrial formation from a completely unknown process was favored. Iron silicides, as a new class of meteorites, have also been considered for a while now.

Let us return to the cosmic connections. Recently, hapkeite (1–2 μm) was found in a meteorite from Koshava, Bulgaria and discovered in the meteorite DAG 1066; it also occurs in a grain from the FRO 90228 ureilite. Fe2Si reported for magnetic spherules in Hungary could be related to cosmic dust or a meteorite impact. Hapkeite was found also in a 7 μm Supernova graphite (OR1d3m-18) from the Orgueil meteorite. A few years ago, naquite, suessite, and xifengite were identified in the Khatyrka CV3 carbonaceous chondrite. An interesting discussion was also triggered on the origin and formation of various iron silicide phases in the aerogel of the Stardust mission. For this Special Issue, we invite recent advances in the investigation of natural iron silicides and their relations to mineralogy. Studies on industrial iron silicides will only be considered if there are direct and informative links to natural minerals.

Insights into the following topics are especially welcome:

• Physical and optical properties
• Terrestrial iron silicides
• Iron silicide in meteorites
• Cosmic relations
• Formation processes
• Geological environments
• Shock metamorphism in iron silicide
• Unnamed iron silicides
• Deep Earth mantle iron silicides
• Earth planets and iron silicides

Prof. Dr. Kord Ernstson
Dr. Pavel Svanda
Dr. Ioannis Baziotis
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Minerals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• xifengite
• gupeiite
• hapkeite
• suessite
• linzhite
• naquite
• ureilites
• cosmic dust
• shock metamorphism
• meteorites
• lunar iron silicides