I came across an ad on Craigslist for some left over firebrick and long story short I bought them .I got them home and realized they are only 8" x 2 3/16th" x 4" a full 1 inch shy of the other firebrick I have and they are much rougher in texture and they weight about 5 lbs. Did i get taken? I never heard of 8" firebrick. The color is darker as well. any thoughts? how can i tell if it is real?