Is it Calcite or Axinite?
(A little article about "flash")

One way to tell the difference between calcite and manganaxinite is to check it for "flash" or brief intense phosphorescence (BIP).  In a darkened room, shine a short-wave UV lamp on the rock and then quickly pull it away.  For a brief moment, the rock will still glow.  It winks out shortly afterward, perhaps a fraction of a second. 

Right now I'm talking about two specific minerals that glow red (calcite and manganaxinite), but BIP can happen with minerals that glow other colors, as well.

Here's a bit of advice.

Don't go overboard & try to get the rock away from the light at breakneck speed.  I've seen people move the light away so fast that, if they were accidentally to strike it against something, it would hurt.   Many times I've seen collectors move the light back and forth repeatedly, at maddening speed in both directions, then declare "yep, the rock flashes." 

You don't need to move the light at 90 miles an hour to test for "flash".  Don't move the light as fast as you can.  Don't even move it half as fast as you can.  You're going to confuse yourself badly if you do.  The idea is to look for "flash", not "blink". 

Calcite's BIP reaction is distinct enough that you can take the rock away from the light fairly slowly (Want a number?  Try 30 cm/s for starters).  I'd estimate it takes as much as 1/2 a second before a typical calcite quenches out after UV exposure;  and I'm pretty sure it takes at least 1/4 second.

If you go too fast, on the other hand, you'll find that manganaxinite itself has a short-lived "flash".  In fact, so does willemite.  ("Willemite flashes!  It must be green calcite!  Stop the presses!")  It winks out pretty quickly after the light is gone, but not immediately.

This point is going to be lost on some people. They are going to shake their heads.  They are going to say I don't know what I'm talking about.  (Optical illusion, human reaction time, post-event neuron firing... name any excuse you want.) 

That's alright.  In the meantime, if you have any rocks that look &   fluoresce like axinite but "flash" when you pull the light away rapidly, you can give them to me.  I'll take those awful "calcites" off your hands. 








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