I'm writing book two in THE ELVEN LORDS series, THE STORM LORD'S DAUGHTER, and I have an elven lady whose magic is with gemstones. Her main ability is to enspell jewels but she is certainly capable of 'creating' her own gems with her magic. But that would require more energy than just digging them up from the earth. And besides, each of the seven sovereignties that the elven lords created in England has been changed according to their magical gifts. So, I needed to know what gemstones she could unearth that were native to England, thereby altering the landscape.
So, all stop on the manuscript and off to hunt down the information. I should say at this point that although I change England with magic, which gives me more leeway with history than a straight historical author, I still need to know the facts before I change them. When I alter something, I don't wish to do it out of ignorance, but with purpose. Call me picky, but I do like to keep the historical aspects of my books as real for my readers as I possibly can. So what gemstones can be unearthed from England? I tried all sorts of search words (which is the key when searching the internet) from natural minerals to lapidary England. Finally I thought of the term, mineralogy and bazinga! I hit the jackpot with this site:
It's amazing! Not only can you search the site for all the minerals found in England (or anywhere else in the world), but you can narrow it down by city/county etc. And each mineral has a photo and description, when it was named, chemical breakdown (I didn't need this, but it was cool!), etc. You might have to look up the definition of each mineral to find out what it was used for, whether to make concrete or pottery, but many of the minerals that were used for gemstones you would recognize by name.
I discovered that quartz is the most common mineral in England (and the world) so I had my answer for my book, and passing this on to save my fellow writers some research time (or hey, to those that love to look at pics of gorgeous stones).