Rough Moonstone (possibly Albite)
Although sold as 'moonstone,' this rough stone is likely a type of plagioclase (play-jee-oh-klayz) feldspar.
'Moonstone' is a trade name used for certain types of feldspar that exhibit visual effects like schiller (a metallic shimmer), iridescence (a rainbow-like play of colours), or adularescence (a soft, glowing sheen).
Stones marketed as 'rainbow moonstone' are often a variety of white labradorite, usually peristerite.
Plagioclase is a group of feldspar minerals with compositions ranging from albite, which is rich in sodium, to anorthite, which is rich in calcium.
The minerals in this group are typically mixtures of albite and anorthite, and their names reflect the balance between the two:
- Albite: Mostly sodium, with very little calcium.
- Oligoclase: More sodium than calcium.
- Andesine: Roughly equal amounts of sodium and calcium.
- Labradorite: More calcium than sodium.
- Bytownite: Mostly calcium, with little sodium.
- Anorthite: Almost entirely calcium.
In geology, the term 'plagioclase' tends to be used because these minerals have a similar appearance and it's not always straightforward to tell one from the other.
Based on their appearance, I believe this rough 'moonstone' is probably albite.
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