//      Compute coordinates.  Allowable range is a box
  //      that sits above the X-Z plane and extends +/-5
  //      in X or Z and 20 in Y.  The color is determined
  //      randomly in red, green, and blue.  The cycle time
  //      is also determined randomly from 1 to 20 seconds.
  
        function addCrystal (value, time, loop) {
          sx = Math.floor (Math.random(seed) * 20) + 1;
          sz = Math.floor (Math.random(seed) * 10) + 1;
          sy = Math.floor (Math.random(seed) * 20)/10 + .1;
          xc = (Math.floor (Math.random(seed) * 20 - 10) * 100) / 100;
          zc = (Math.floor (Math.random(seed) * 20 - 10) * 100) / 100;
          yc = (Math.floor (Math.random(seed) * 12 + 1) * 100) / 100;
          rd = (Math.floor (Math.random(seed) * 100)) / 100;
          gn = (Math.floor (Math.random(seed) * 100)) / 100;
          bl = (Math.floor (Math.random(seed) * 100)) / 100;
          tt = (Math.floor (Math.random(seed) * 190)) / 10 + 1;