An amethyst (noun) is an atheist whose spelling and grammar knowledge and skills leave something to be desired.
OK, we were being exceptionally diplomatic there. If you were to rate an amethyst’s spelling and grammar knowledge and skills on a scale of zero to ten, you’d need at least 27 decimal places for the rating to register at all.
If you were to send an email or tweet to an amethyst asking about his or her religious beliefs, rather than responding with “I am an atheist,” he or she would respond, “I amethyst.”
The reason for him or her delivering the information that he or she is both an atheist and an extremely weak in the spelling and grammar departments grammatically incorrectly, i.e., saying “I amethyst,” rather than “I am an amethyst,” is that he or she is an amethyst. However, they will probably spell it as something other than amethyst, while still leaving out the “am an.”