Made of shale

• Dark bluish-gray
• Having a bluish-gray hue
• Bluish-gray in color
• Grayish in color
• Of a grayish hue
• Like an overcast sky
• Dull blue-gray
• Dark blue-gray

WordNet Word definitions in WordNet
adj. resembling or containing slate [syn: slatey ] of the color of slate or granite; "the slaty sky of dawn" [syn: slate-gray , slatey , stone-gray ] [also: slatiest , slatier ]

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Slaty \Slat"y\, a. [From Slate .] Resembling slate; having the nature, appearance, or properties, of slate; composed of thin parallel plates, capable of being separated by splitting; as, a slaty color or texture. Slaty cleavage (Min.), cleavage, as of rocks, ...