Where gemstones lie scattered on the ground

I have been in Spain since early January and missed the worst of the UK floods and storms. While there I experimented with my first free Kindle Select promotion and saw more than 2,000 downloads of my short story thriller 'One False Move'. I have no idea if this is good or bad but the half-expected spike in sales of other books never really materialised.
I also responded to requests from agents to take a look at 'The Immortality Plot'. One agent suggested changes and edits that I agreed with but I still await his final appraisal (hopefully with an offer of representation).
Did a lot of beachcombing and travelling out and around Almeria and the Cabo de Gato with its unspoiled beaches.
My wife collects stones to turn into mosaics and has an interest in geology. So we visited a caldera (sunken volcano) near Nijar because we met some student geologists from the University of Hamburg who tipped us off that we could pick up garnet gemstones on the ground. And it was true. Most of the stones are small, about the size of peppercorns but others are larger. Somewhere on the slopes of the caldera, further back inland, we reckon we might discover some really sizeable gems. No idea of value, doubt if they are worth much, but when tumbled and polished they could make beautiful earrings or even a necklace.
If anyone knows the value of garnets do let me know.
I am now considering setting my next Mike Delaney thriller partly in Andalucia. I love the arid beauty of the place, fantastic landscapes and watching the sunset as swifts duck and dive while sipping a very cold beer.
Hasta Luego