Marshite from Broken Hill, Australia
Contributed by: Michael Crawford
Date: Aug 24th, 2025
Locality: Broken Hill, Broken Hill district, Yancowinna Co., New South Wales, Australia (See on Mindat)
Size: 7 x 9 mm
Description:
Marshite is an uncommon copper iodide (CuI) mineral. This small marshite specimen comes from the Broken Hill, Yancowinna County, New South Wales, Australia. This specimen is comprised almost entirely of tiny crystals of red marshite. The red color is due to inclusions of bright red chalcotrichite. Marshite is a secondary mineral formed from the oxidation of the original sulfide deposit by circulating groundwater.
It is very unusual for a copper mineral to fluoresce. Copper ions have two oxidation stqtes. Cupric copper (Cu2+) is the most common oxidation state and the most stable form. Cupric copper is usually a quencher of fluorescence. Cuprous copper (Cu+) is the second oxidation state, and it is the ion that bonds to iodine to form marshite. Marshite’s red fluorescence is intrinsic due to the cuprous ion. The red fluorescence is brightest under longwave illumination. It also fluoresces under midwave and shortwave UV light. The longwave emission spectrum is unique. It has a sharp violet peak with a maximum at 409 nm and the broad peak in the red region with a maximum at 685 nm.
Summary of luminescence responses:
Marshite (Mindat) (RRUFF)
- Fluorescence under Longwave (365nm LED) UV light: Red
- Fluorescence under Longwave (365nm LED) UV light: Blue