A 2D game asset sprite of a single square wall block, minimalist flat design. The visual style is strictly monochrome noir, using only a solid, uniform matte charcoal gray color for the entire block. The surface must be completely smooth and flat, without any texture, patterns, gradients, or 3D shading. The visual cue for absorption should come from its extremely dull, light-absorbing matte finish. Sharp, clean, perfectly straight edges. Orthographic front view, perfectly centered, isolated on a pure solid white background for easy alpha masking.