The first "mana rock" artifacts other than Alpha's broken Moxen to see serious play were the so-called Mana Diamonds of Mirage. Despite their enters-the-battlefield-tapped drawback and their 2-mana cost, they provided the best acceleration that non-green decks could get in the early days of Magic. They haven't been seen in reprint form since Seventh Edition; but apparently they're making it back to paper Magic soon, according to the Facebook page of a fantasy artist who's painted new Mana Diamond art for the entire cycle.
I just got the go-ahead to post a whole lot of good stuff! These are included in MTG's Duels of the Planeswalkers 2015 (for MGTO, released today) and will be physically printed later in another set. Charcoal Diamond, Fire Diamond, Marble Diamond, Moss Diamond, and Sky Diamond. All 12 in by 9 in, oil on illustration board.
Now, these particular artifacts don't seem to fit in Tarkir block all that well, based on what we know about its themes (besides, R&D likes to make new mana rocks for each block rather than reprints, which tend to be reserved for core sets), and the new art seems to still refer to Jamuraa - in other words, they're still associated with the original setting. The "physically printed" comment thus likely refers to a supplemental product of some sort, probably 2014's official Commander decks since those are guaranteed to come out each year, but also possibly a new Planechase product or something else of the sort.