Niter, along with Nitratine, are unusual minerals belonging to the nitrates group. These two nitrate minerals can be visually indistinguishable, with the ancient term Niter used to describe both Niter and Nitratine. Nitratine is actually the more prevalent and economically important member of the group.
Niter is a very fragile mineral, and is poorly represented in collections. Its solubility in water restricts its occurrence to caves where it receives protection from rain. Niter often forms as powdery growths on cavern walls, and doesn't usually form in good crystals. Large crystals are not natural, and are easily grown synthetically.
Niter original name source is from the ancient Hebrew word "neter", where it is described as cleaning agent in biblical sources.