Ruby is the most expensive among all corundum gems because it contains chromium (Cr, χρώμιο), because the output of ruby is very small. Σε σύγκριση με το ζαφείρι, the output is only 1/5 από αυτό του ζαφείρι; and ruby is usually very crystallized. There are not many rubies larger than 5 καράτια. Rubies larger than 10 καράτια [...]
