Occasionally, a rock is called "A Beryl Rock" ... other times, it's just "Beryl Rock" ... so the copy sometimes tells me I just mined "an A Beryl Rock". Not sure why some are right and others aren't. Also noticed on Sparkly Rocks.
We don't have immediate plans to work out some of the article discrepancies with items in the game. In many of these cases, the items are named in our system as "A [type] Rock" (just giving a generic example) and there isn't a mechanism to parse articles for each use. At a later date, we'll do this, but for now, we're leaving them as is.