Small World Slate & Stone is proud to offer these unique natural slate/quartz stones. They have been sourced, washed, hand picked, and packaged by a family owned business in the USA. These stones are easy to incorporate into your tank or enclosure and pair beautifully with our smaller and larger solid grey stones and gravel to give a more realistic look to your tank. Create caves, berms, water falls and walls in your aquarium, terrarium, paludarium, vivarium or miniature garden. Thoroughly rinse all stones before placing in your habitat. Absolutely no coatings on this or any of our stone. Slate is inert and aquarium safe. In the quartz portion of these stones (not the slate), there are carbonate minerals (marble/limestone) which can raise/buffer pH. This is ok with most aquarium tank inhabitants that prefer 7.5-8 pH. Use with caution with species that prefer very low (acidic) pH.