Sorry guys, have to disagree.
This rock is karst (eroded) limestone; most is, in fact, old coral reef. If you look at some pieces very closely, it has a variety of marine fossils (mostly snails) in it. Keep in mind that most of Texas used to be shallow ocean at one point, which is why it is a fantastic place to collect fossils.
It is commonly used in cichlid tanks because it keeps pH HIGH (same as we desire in salt tanks), and is really not all that different than LR in its chemical composition. It is not quite as porous, but is a good base rock if you can't afford all LR.
It is quite commonly sold for SW tanks. You may soak it for awhile to remove any soil and dust, but, IMO, it is fine for saltwater tanks, assuming it is clean.
The nitrite thing is likely a typo, they are probably talking about freshwater pH....due to salt in our saltwater, the water has a higher pH and the limestone additionally helps this (just as limestone aka carbonate sand or crushed coral does). The limestone will not lower the pH in a saltwater tank to 7.8, but will help buffer 'up' the pH of (normally lower pH) freshwater tanks.
But, to my knowledge, it does not possess any 'miraculous' characteristics and is not particularly 'holy' but holey ba...dum dum. LOL
OK, its late