The Morgan silver dollar is a precious metal coin minted in the late 19th century into the early 20th century. They are collectable and thus occasionally counterfeited. I’ve recently analysed genuine and counterfeit silver dollars using x-ray fluorescence (XRF) – here I’ve used a Rigaku NEX-CG ED-XRF instrument using a “fundamental parameters” estimation mode. There’s some work to do to optimise the system for these samples – it’s not something we usually work on!
Anyhow, the counterfeit seems to be brass, plated with silver. The real thing has a specification of 90% Ag, 10% Cu.
| Element | Specification | Genuine | Counterfeit |
| Ag | 90 % | 92.3 % | 27.2 % |
| Cu | 10 % | 6.6 % | 43.1 % |
| Zn | 0 % | 0.0 % | 26.0 % |
I’ve also analysed some old “round-pound” £1 coins. These were demonetised in 2017, because nationally around 1 in 30 of the coins in circulation were counterfeit – I’ve heard that in some areas, the number could have been as high as 1 in 5. I’ve found that genuine and counterfeit coins have a pretty similar Nickel-Brass metal, but can be easily distinguished by their Pb content – around 1.5 % in counterfeits, and negligible in genuine coins. The Pb is added to improve malleability.
| Specification | Genuine (1 σ, n = 8) | Counterfeit (1 σ, n = 2) | |
| Ni | 5.5 % | 6.0 ± 0.5 % | 4.9 ± 0.1 % |
| Cu | 70.0 % | 69.9 ± 0.6 % | 67.3 ± 0.4 % |
| Zn | 24.5 % | 23.1 ± 0.9 % | 25.1 ± 0.1 % |
| Pb | 0.0 % | 0.0 ± 0.0 % | 1.4 ± 0.6 % |
I’m going to develop this into part of an outreach activity that uses our Niton Handheld XRF. I’m planning demonstrations of contaminated vs. uncontaminated soils, and some other geological samples.