Hello there, i picked this is up with a decanter a couple of days ago, the decanter is on one of my posts and dated to roughly the same age as this. It's pressed glass, lead crystal and has lot's of "grit" i think you call it (white particles within the glass). There is no wear at all on it anywhere even on the facing edges or damage with just a tiny amount wear to the base, i'ts dated either I for 1872 or P for 1877 there are no other makers marks that i can see, i'm not really sure what it's for.
It measures 10 inches across the rim and 7 inches across the base, regards Chris.