Weird samoa proof measurements

Hello,

I have bought this coin, which is proof, so it means it should be silver 925.

Numista lists dimensions as:

Weight 15.40 g

Diameter 32.4 mm

Thickness ?

I'm getting 

Weight 16,63 g

Diameter 32.3 mm

Thickness 2.3 mm

Magnet doesnt stick

Question is that a genuine silver coin? AI says it can't be silver according to calculations by formulas… So im a bit confused

AI isn't very smart.  Where did you measure the thickness? On the rim or in the center of the coin where both sides are flat?  The rim is going to be thicker than the rest of the coin which would greatly affect (lower) the calculated density.  .925 silver has a density of about 10.35 g/cc.  For your weight and diameter (assuming they were measured accurately) the thickness, if it were an exact cylinder, would have to be 1.95 mm.  You have everything you need to measure the density directly and prove or disprove it is actually silver.  https://en.numista.com/numisdoc/determining-the-metal-of-a-coin-27.html

rsirian1

AI isn't very smart.  Where did you measure the thickness? On the rim or in the center of the coin where both sides are flat?  The rim is going to be thicker than the rest of the coin which would greatly affect (lower) the calculated density.  .925 silver has a density of about 10.35 g/cc.  For your weight and diameter (assuming they were measured accurately) the thickness, if it were an exact cylinder, would have to be 1.95 mm.  You have everything you need to measure the density directly and prove or disprove it is actually silver.  https://en.numista.com/numisdoc/determining-the-metal-of-a-coin-27.html

Thanks! Thickness on the rim was around 2,4mm but digital calipher accuracy is +-0,2mm I did litte experiment and found out the weight in the water 1,39 grams. The calculator on the website refuses to divide but im getting 16,6/1,39=11,94, which is above the silver on the graph. So I assume its density higher than silver? just interesting how it varied from the ngc, numista weight and no thickness appears to be provided

I would attribute the high density you measured to some experimental errors but you can be sure your coin is silver.   Id be pretty sure it isn't Thallium or Palladium.

rsirian1

I would attribute the high density you measured to some experimental errors but you can be sure your coin is silver.   Id be pretty sure it isn't Thallium or Palladium.

I see. And if the measurements I did are somewhat close to the reality would it be factory error of thick planchet, wrong planchet or different alloy? Probably only xrf knows..

Thickness or diameter doesn’t matter measuring the density that way. I highly doubt it’s not silver.  Redo the density measurement three or four times always starting from the beginning. 

rsirian1

Thickness or diameter doesn’t matter measuring the density that way. I highly doubt it’s not silver.  Redo the density measurement three or four times always starting from the beginning. 

Interestingly, few online sources list a higher weight than Numistas, but still less than what I measured. For example, one source shows a diameter of 32.40 mm and a weight at 16,11 other shows 32,4 diameter and 16,15 grams of weight near the physical properties section. Nobody writes thickness, unfortunately.

I may try to repeat density tests..