Siderite

Siderite is iron carbonate, an important iron ore of a light yellowish brown color, but sometimes also gray, yellowish brown, greenish brown or reddish brown. Ours is a light yellowish brown brought directly from its source in Kaluzhskaia Oblast, Russia.

Pigment Information:
Siderite

Alternate Names: sparry iron, spathic iron Color: Brown Colour Index: Not Listed ASTM Lightfastness: Not Tested Hardness: 3.5 - 4.5 Density: 3.9 Chemical Formula: FeCO₃

Siderite is carbonate of iron, an important ore of iron occurring generally in cleavable masses, but also in rhombohedral crystals. It is of a light yellowish brown color, but can also be gray, yellow, yellowish brown, greenish brown and reddish brown because of impurities or the alteration to goethite (See this pigment). Siderite is named for the Greek word for iron, sideros. It forms a series with closely related minerals rhodochrosite, MnCO₃ and magnesite, MgCO₃. The iron has little effect on most structural properties such as crystal form, but does affect properties such as density, color, and hardness. Siderite occurs mostly in sedimentary and hydrothermal environments, although it is also found in some igneous pegmatites (a variety of granite occurring in veins). Other minerals associated with siderite include iron sulfides, quartz, cerussite, ankerite, dolomite, goethite, cryolite, limonite, barite, pyrite and sphalerite.
Origin: We make our siderite from minerals obtained directly from its source in the Kaluzhskaia province of Russia.
History of Use: A survey of literature did not reveal any direct evidence of siderite among historical pigments. However, since siderite is closely associated with iron oxide pigments such as goethite (ochre), it may be safe to assume that it has been in use for as long as ochre pigments.
Permanence and Compatibility: As an earth pigment, siderite is also among the most permanent pigments in the artist's palette. Although it is a carbonate and hence reactive to acids, it can be safely used in all media.
Oil Absorption and Grinding: Siderite absorbs a moderate amount of oil during dispersion and forms a good flexible film.
Toxicity: Siderite is not considered toxic but care should be used in handling the dry powder pigment so as not to inhale its dust.

Read cautions about handling pigments