igneous

Ferrocoke or Slag

Anthropogenic pyrometallurgical residue

Hardness: 6-7 (Mohs scale), Color: Dark grey to charcoal black, Luster: Metallic to dull, Structure: Vesicular (contains air pockets) and amorphous/glassy, Cleavage: None/Conchoidal fractures, Specific gravity: Variable (typically 2.5-4.0)

Identified April 2, 2026More igneous →

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Physical properties

Formation & geological history

Formed as a byproduct of historical or modern industrial smelting (specifically iron production). It is created when fluxing agents melt together with impurities from iron ore and fuel (coke or charcoal) and then cool rapidly above ground.

Uses & applications

Historically used for road aggregate, railroad ballast, and in some forms of cement production. In modern times, it is often studied as an industrial archaeological artifact.

Geological facts

Slag can often be mistaken for meteorites due to its dark color, metallic sheen, and pitted surface; however, the presence of bubbles (vesicles) proves it was formed at Earth's surface pressure.

Field identification & locations

Identify by looking for air bubbles (vesicles), a glassy 'conchoidal' fracture pattern, and a high density. It is often found near old railways, industrial sites, and riverbanks near historical foundries.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral