VEVOR Black River Rocks, 1-2 inch 15 lbs, Smooth & Polished Natural Pebble Stones, Decorative Garden Landscaping Stones, Paving Plant Rocks for Fish Tank, Flower Pots, Water Fountains, Pathways, Backyard
Are these black rocks naturally all black? Do they have anything added to them like pigment, ink, or resin or anything? Are they just 100% natural rock?