Coins were not in use? So what was a shekel? A unit of weight?
Click on the above picture. There’s a short video that provides the info.
You are correct. The ancient Kdm of Lydia was later, and the discovery of the touchstone to assay gold content, coupled with a big gold strike, resulted in the first coins (contrary to what is sometimes claimed).
coins lydia site:freerepublic.com
Yes, the article says that "shekel" was a unit of weight used in the marketplace for anything bought or sold -- before it became the name for a coin.
It also says that something was weighed and collected as a tax but does not identify the substance that was weighed, so perhaps it is not known -- "One of the uses of the shekel weight system during the First Temple period was to collect an annual tax of half a shekel dedicated to the sacrifices and upkeep of the Temple."
First coins probably Lydian lion coins in about 580 BCE (Ephesus temple). The first Jewish temple in Jerusalem was built 987 (and destroyed 586-587, right about the time those first known coins were invented 616 air miles to the north. And those coins didn’t circulate much as they were a local thing and given too high a valuation to be useful in daily trade ir commerce. FYI.
Yes, it was a defined weight.
https://www.convert-me.com/en/convert/history_weight/bibshekel.html?u=bibshekel&v=1