[Hallicrafters] SX-111 Crystal Calibrator

[Bill]

Just got an SX-111 in very good condition.  Upon internal
inspection, I noticed a "Tube" type I have never seen.  Upon
closer inspection, I noticed it was something else and thought
it might be a crystal in a glass envelope.

It looks like a mid-sized rectifier tube and has a bakelite base.
Anyone know what it might be.  Is it a crystal in a tube envelope?
Is it in a vacuum?

K2WH