In the post about the Amethyst Crystal, I mentioned how quartz is normally white or clear unless other elements creep into the SiO4 silicon–oxygen matrix. I mentioned how amethyst is quartz that has been colored purple because of the presence of iron. Citrine is also colored yellow-golden by the presence of iron, so how can some stones become amethyst and some become citrine?
The answer is: heat 🔥
If amethyst is heated, the purple color gives way to yellow and orange hues because of the change in the oxidation state of iron within the crystal. Most citrine that occurs in nature is a pale yellow. If low-grade amethyst is intentionally heated properly to form citrine, though, it usually turns a darker golden color, orange, or reddish-orange. This crystal, therefore, was likely heat-treated, but is still no less beautiful to me than if it had come from the earth looking like this.
The bottom of the crystal is a wonderful opaque white mass of quartzy goodness, with all of the included iron residing in the other end of the piece.
It may sound rather odd, but I cannot think of citrine without thinking of 
The iron-rich top of the crystal is translucent, allowing light to pass through, although it is not fully transparent. There's a lot of "stuff" to see inside the top of the crystal: bits of silicon that were not oxidized to become part of the crystal, proper, and it forms several planes and small bits that reflect light beautifully!
And here is one final look at the citrine crystal, posing alongside its traveling companions from the package which brought it to me:
A big Thank You! to 
three beautiful crystals to add to my collection! 🤗
SOURCES
1 AmethystGalleries: Citrine
2 Minerals.net: Citrine
3 Wikipedia: Ametrine
4 Wikipedia: Quartz
14-Nov-2019
