From: 10th Ore Zone, Kerr McGee Mine, Carlsbad, New Mexico
Size: 3.8 x 7.3 x 4.2cm
This is a very affordable blue halite on sylvite matrix specimen from Carlsbad, New Mexico. Specimens with cubic crystalline blue halite are becoming harder and harder to find, and this one has one primary blue halite crystal measuring 1.9cm long, and there are several other small blue halite crystals around the specimen. On the top area is some regular clear halite that is also cubic in nature, and you can see through it like a window to reveal the matrix under it. This specimen comes with a labeled acrylic display base.
The blue halite would have formed first - tens of millions of years ago. The surrounding Sylvite mineral contains radioactive Potassium 40 which has an incredibly long half-life of 1 billion years. This means the radiation is so low that geiger counters have a hard time even picking it up. Potassium 40 is also found in bananas, but the radiation is so low that it's harmless to ingest. That being said, over tens of millions of years this low radioactivity takes its toll on the halite, effectively altering the crystal lattice which gives it its blue color. The blue is not chemical - it's just a result of radiation on regular old table salt. The clear halite grew in more recently, and it hasn't had time to be turned blue by the potassium in the Sylvite.