Looks a bit like concrete with subtle specks spread around the pattern.
Source Mladjan Antic
A repeating gloomy background image. This one consists of a pattern of black chains layered on top of a dark textured background.
Source V. Hartikainen
Prismatic Abstract Line Art Pattern Background 2
Source GDJ
I asked Gjermund if he could make a pattern for us – result!
Source Gjermund Gustavsen
Prismatic Geometric Pattern Background 2
Source GDJ
Remixed from a drawing in 'The March of Loyalty', Letitia MacClintock, 1884.
Source Firkin
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
This is a seamless pattern of regular hexagon which has a honeycomb structure.
Source Yamachem
A repeating background with wood/straw like texture.
Source V. Hartikainen
Prismatic Polka Dots Mark II 3 No Background
Source GDJ
A seamless background pattern with impressed gray dots.
Source V. Hartikainen
Scanned some rice paper and tiled it up for you. Enjoy.
Source Atle Mo
Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
Prismatic Polka Dots Mark II No Background
Source GDJ
Simple wide squares with a small indent. Fits all.
Source Petr Šulc.
There are many carbon patterns, but this one is tiny.
Source Designova
From a drawing in 'Heroes of North African Discovery', Nancy Meugens, 1894.
Source Firkin
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin