Gem is higher than Choice. It means the coin exhibits strong strike and sharp details, while choice is slightly under that.
The conversion to the Sheldon Grading Scale would be something similar to this MS63-MS64=Choice MS65= Gem
To the OP, It is also Important to note that a Gem coin needs more than a strong strike and sharp details. When coins are graded luster plays a huge role as well as marks on the coin. A Gem coin might have the same strike and details as a choice coin but possesses more luster. It might also have the same amount of luster strike and details but dont have as many marks as the choice coin. Eye appeal would also play a huge role in the grading process which means That maybe we have two identical coins (Luster Strike Toning) except one has a mark in the open field and is very noticeable, the other has the same exact mark but its hidden in the hair or feathers and doesn't take much of the appeal away. Eye appeal also refers to but is not limited to the toning, in most cases toning can add or subtract points.
MS-60 = BU MS-61 = Select BU MS-62 = Very Select BU MS-63 = Choice BU MS-64 = Very Choice BU MS-65 = Gem BU MS-66 = Very Gem BU MS-67 = Superb Gem BU MS-68 = Very Suberb Gem BU MS-69 = Almost Perfect MS-70 = Perfect
Well Put and sometimes People take out the very and would just doing something like this Gem BU Gem BU+ Superb BU
Terminology used for mint state coins in Heritage Auctions' US coin catalogs: MS63: Select MS64: Choice or Near-Gem MS65: Gem MS66: Premium Gem MS67: Superb or Superb Gem MS70: Perfect Proof coins have the same adjectives, but need to also be described as "Proof". We will never use the term "Select" on a coin grading below MS63 or PR63. Mint State or Proof coins grading above or below those ranges will not have grades described by adjectives; we simply use the numerical grade. This represents official cataloging department procedure and not necessarily the opinions of the poster.
