Hi Silverclaws.
Check this website
http://www.saudiaramcoworld.com/issu...f.a.thaler.htm
for history of the Thaler. This coin was the major source of silver in the Middle East, for weapons decoration, and also jewelery making. It made its way there by way of traders, and also as "bribe money" by the then Colonial Powers, and there was not, to my knowledge, any arrival by shipwreck, though no doubt there were also plenty of those! If you go to GOOGLE there are many other listings giving history of the coin. It weighs 1 oz Troy, and is, I believe very close to pure silver. The edge is knurled in a special way, so there was no possibility that the weight could be reduced by some dishonest individual. They were used also as a trading item, with I would expect, the value being set by the economic climate at the time. These coins are still easy to obtain thru dealers and a cheap price, and I have one as a curiosity with my collection.
Hope this is of interest.