I'm not sure about amulets that are enchanted but amulets that are strung/unstrung don't have the correct alch prices.
I have a lot of amulets and I would like to alch some of them u c.
The alch prices for the strung and unstrung are the same.
Sapphire amulets:
High Alch: 540 Coins; Low Alch: 360 Coins.
Emerald amulets:
High Alch: 765 Coins; Low Alch: 510 Coins.
Ruby amulets:
High Alch: 1215 Coins; Low Alch: 810 Coins.
Diamond amulets:
High Alch: 2100 Coins; Low Alch: 1400 Coins.
On an unrelated note, none topaz, opal, and jade gems still can become crushed gems when cutting them. That shouldn't happen.