Are Aragonite and Calcite the Same?
The short answer, no. I’ve seen this out on the web. I get it. They look quite similar but they are NOT the same.
While both do have the same chemical formula, CaCO3, their atoms get stacked in different configurations. That is, they are polymorphs (two or more chemically identical but crystallographically distinct forms).
Aragonite has an ortho-rhombic structure and Calcite a trigonal structure.
Rhombic Crystal Systems are all those that have a diamond shaped inner structure. Rhombic minerals can form either Aragonite, Peridot or Topaz, but sometimes they also form in Hexagonal shapes (3 Rhombuses fitted together that form a hexagon). When they form this way they are called pseudo-hexagonal. Aragonite would fall into this group.
Trigonal Crystal Systems can take the form of pillars like Tourmaline or Emerald. Many popular favorites fall into this category. Agates, the Quartz family, Aventurine, Bloodstone, the Chalcedony family, Calcite, Chrysoprase, the Jasper family, Rhodochrosite, Tiger’s Eye, Tiger Iron and many more.