Rocks on display tank

[discusage]

I am setting up a display tank with some driftwood and river sand. I want to put slate rock as additional display on my tank. Is it safe to do that? Thanks.

[ILLUSN]

generally yes, slate is generally unreactive.
remember slate begins as shale shich is a sedmentary rock and thought heat and compression it becomes slate.

if you are really worried do an acid test put a drop of acid onto your slate, if it fizzes, bubbles or foams you can give it a wash in dilute acid, let it dry and try again. If it happens on the cleaned slate dont put it in your tank as it will bugger your water chemistry.