phosphosiderite is pretty strange to work with but a really nice violet purple color.

If your camera lacks manual controls, you might try a darker background.

The first one looks like wonderstone.

I had an archeologist over for dinner some years ago, but I forgot what he said it was.

I've reached a point where I can simply not display all the wonderful specimens that we have collected over the years.  Before I list some of these I would like to identify them.  I bought these at an auction in which the original owner had passed and many of the specimens were misidentified.  For some reason Photobucket resized my shots and yellowed the color.
http://s1376.photobucket.com/user/seber061seber06/library/?sort=3&page=1

It certainly looks like condor to me.

The difference between dryhead and teepee canyon is only seen in the matrix.  Dryhead is found with a chocolate brown matrix while teepee canyon has a tan matrix.  The orange and crystal sections are identical.
  I've included a bola and buckle of dryhead for comparison.  Sorry, I couldn't find any photos of teepee canyon.

I prefer Kroil as well.  It is available directly from the manufacturer or from McMaster.com

Start at about half the total height and see how you like it.  I generally go a bit less, but no set dimension.  What is more important is that it is the same all the way around.  This can take a lot of trial and error on cabs with points.

Certainly correct on the dryhead and teepee canyon.  As far as size, the largest I've personally collected was 14" but I've seen some as large as three feet across.  Patterns can be so large that cabs are not possible except as solid color.

It is not necessarily tough.  Diamond interacts chemically with iron when heated.  The diamond is converted to carbon.  If you can keep it flooded you should find it easier to work.

The last time I bought aventurine rough was maybe 5 or 6 years ago.  The quality was better than those cabs and if I remember correctly, I paid $2/lb.  These days nothing is less than 3$/lb. but it should still be among the cheapest recognized material.  If I could manage prices like that, I would have retired many years ago.

In clear crystal form the color defines the gemstone.  IE emerald, goshenite, bisbyte, heliador, morganite, aquamarine and a few others.  On the other hand, the biggest use by far is as raw ore for berylium.

Aventurine is calcedony.  It will cab like any agate or jasper.

WD 40 is not meant to be a lubricant.  Using it to free anything will be very frustrating.  For that, use PB Blaster or Kroil.  In this case however, that will have no effect.  The bearings are press fit.  Put a socket over the end of the shaft up against the housing.  It must be large enough so that the bearing can pass into the id of the socket.  Use a press to push the other end of the shaft and the bearing should pop out.  If you need to push very hard, then support the housing from one end to the other inside to prevent collapsing the structure.  It is possible the the shaft can move without removing the bearing.  I have not experienced this, but it can happen.  If it does, go ahead and push it out then use a shouldered shaft to push out the bearing.  Whatever you do, do not use a hammer.  If you have no way to press out the shaft, take it to a machine shop.  A good machinist can do this in just a few minutes and should be only a nominal charge.