The sample arrived, very nice crystal, with cracks along cleavage planes. One of the cracks affects more than half the crystal. The one along the edges of the crystal probably can not be “polished” out. I would suggest filling the cracks with oil or resin, perhaps “Opticon.” This would treat the crystal to make the cracks less visible.
As a geologist, the term “Iceland Spar” refers to calcite crystals found in one particular location in Iceland. The sample you sent has a sticker that says: “Made in Brazil.” So, in a very strict interpretation, that sample is not “Iceland Spar.” However, it is a very nice sample of optical grade calcite.