indigo is actually a plant used to make the dye indigo. I only know that because I just had to teach about the crop being grown in South Carolina when a girl named Eliza Lucas developed it as a second cash crop to rice. Gee, aren't I just a wealth of information! lol j/k

My favorite "I" mineral is Icelandspar because you can put on a piece of paper and it doubles the image!

How about Jade for "J"