Rock blending in with substrate?

[NeonFlux]

What kind of rock would blend in with eco-complete?

[247Plants]

black lava rock would work. Basalts are pretty black.

[NeonFlux]

Lava rock? Hm! Where can I get lava rock

[Bk828]

you talking about adding large rocks or more gravel??

Lava rocks would blend in nice (not those tufa type of lava rocks)
Zebra stones would blend in. Though one would want to make some contrast if they are using larger stones for the scape

[rsanz]

I find that slate, once it "ages" and gets a little algae/organic matter on it, colors up nicely and blends well with the black substrate.

My tank uses flagstone (similar to slate...might even BE slate, lol):

http://farm4.static.flickr.com/3017/2806917211_76c8066d6a_o.jpg

[247Plants]

theres some pretty dark granites out there too.

[Darkness9876]

Flagstone is a style of rock more than a type of rock.
Yours does appear to be a kind of slate.
Huh so an interest in geology does come in handy...... Btw that tank is amazing. Simple to the point and absolutley beautiful. Kind like my girlfriend.