Here are the stats on Sapphire Gems from the folks that have the Trademark on them; https://hoovershatchery.com/sapphiregem.htmlHeavier than a leghorn and lighter than rocks and Wyandotes. I'll look it hope. I recently read it. They are supposed to kick out 290 eggs a year which is my only worry.
I must have been reading about another newer breed and confused that with the Sapphire Gems.