The mislabelling between Blue Calcite and Celestite is a really common one that pops up with both online shops and high street shops, and it's important to know which you're buying. Many wholesalers are selling Blue Calcite as Celestite, which is then passed down the supply chain so many shops end up furthering the confusion.
Blue Calcite is a beautiful soft blue colour, and looks very dreamy when polished into sphere, palmstones, freeforms and tumbles. This exact same material is being labelled as polished Celestite - beware it's not!
Raw Blue Calcite:
Polished Blue Calcite:
Celestite very rarely forms in large single crystals, and tumbled Celestite does exist, but it's comparatively rare due to the size of crystal needed. Examples of Celestite geodes can be seen in the next two photos below.
Celestite spheres also exist, but they are geodes polished into a circular shape rather than a large mass. The first photo is of a true Celestite sphere, taken from mineralminers.com, and the second photo is of a Blue Calcite sphere being sold as Celestite on AliExpress.
One easy test to do is to compare the weight - Celestite is a lot heavier for it's size than Calcite (density), so a sphere of Celestite would weigh 1.45 times the same size Blue Calcite sphere.