
Based on the provided information and standard numismatic specifications, a 1917 Walking Liberty half dollar is composed of 90% silver. One of the supplied sources explicitly states the coin was "Struck... in 90% silver."
To provide a more detailed analysis, the total standard weight of a Walking Liberty half dollar is 12.5 grams. With a composition of 90% silver and 10% copper, the actual amount of pure silver contained within the coin is 11.25 grams. This is equivalent to approximately 0.36169 troy ounces of fine silver. The copper was added to the alloy to increase the coin's hardness and durability for circulation. It is important to note that this weight applies to an uncirculated coin; coins that have experienced wear will have slightly less total mass and therefore a marginally lower silver content.


