Arsenopyrite, Tolwong Mine, Marulan, New South Wales

Mineral Matters #619

The Mineral of the Week Facebook Group current theme is arsenic-bearing minerals.

Arsenopyrite, formula FeAsS, is a very common sulphide mineral. I can even find arsenopyrite within a kilometre or two of my house. It is the most common arsenic mineral and has been an important ore of arsenic.

Arsenopyrite is often found in hydrothermal veins and pegmatites, associated with other sulphide minerals such as pyrite, galena, and sphalerite. It is also found in some metamorphic rocks.

The Tolwong Mine is located in the steep Shoalhaven Gorge area of New South Wales, Australia. It is part of a series of small mines originally established for gold mining, and is situated on the eastern side of the Shoalhaven River, approximately 10 kilometres south-southeast of Marulan.

The mine is known for a variety of minerals, including arsenopyrite, bournonite, calcite, cerussite, chalcopyrite, fluorite, galena, muscovite, pyrite, quartz, scorodite, siderite, sphalerite, stannite, and wurtzite.

A two-part article was published last year in issues of the Monthly Mineral Chronicles (volume 7, issues 3 and 4).

Below: Arsenopyrite and stannite, Tolwong Mine, Marulan, St Vincent Co., New South Wales. Width of view 3.33mm.