The flame test is where a sample is burned in a flame and gives off a certain color. For niter the flame should be violet, an indicator of potassium, and for nitratine the flame should be yellow, an indicator of sodium. Nitratine was an important source of nitrates for fertilizer and other chemical uses including fireworks. Nowadays, fixed nitrogen from the air has all but replaced nitratine as the main source of nitrogen. An interesting side note is that discarded specimens of nitratine were said to have been thrown into a garden and this is how the importance of nitrates in good plant growth was first discovered.
Color is white or gray, sometimes with tints of red-brown or yellow.
Luster is vitreous. Transparency crystals are translucent to transparent. Crystals are rare, but when found are in the form of rhombohedrons similar to calcite's crystals. Cleavage is perfect in three directions forming rhombohedrons. Fracture is conchoidal.