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What metal won't dissolve in aqua regia

I discovered a metallic plating on a crucible after burning its organic contents at 550 °C. After following US customs guidelines for the analysis of metal coatings, I have discovered this coating is not soluble and remains present in solution in Nitric acid, Hydrochloric acid, and aqua regia (1:3). I certainly don't believe I am testing for any noble metals. Any ideas?

Katherine Heilman
graduate student - Frederick, Maryland, USA
2006

Rhodium

Iridium

A. To my knowledge Rhodium is the only metal that is not soluble in aqua regia.

Guillermo Marrufo
Monterrey, NL, Mexico
2006

A. I found this on the table: "Iridium is not attacked by any of the acids nor by aqua regia, but is attacked by molten salts, such as NaCl and NaCN". I don't know but I was told of two more that won't have a reaction.

Chris Morlock
- vernal utah usa
June 27, 2015

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