Brushed aluminum, in a bright gray version. Lovely 2X as well.
Source Andre Schouten
A light gray wall or floor (you decide) of concrete.
Source Atle Mo
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Looks like an old rug or a computer chip.
Source Patutin Sergey
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A mid-tone gray pattern with some cement looking texture.
Source Hendrik Lammers
Recreated from a pattern found in 'Az Osztrák-Magyar Monarchia irásban és képben', 1882. To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Prismatic Rounded Squares Grid 3 No Background
Source GDJ
Remixed from a drawing in 'Incidents on a Journey through Nubia to Darfoor', F. Ensor, 1891.
Source Firkin
Background Wall, Art Abstract, Block Well & CC0 texture.
Source Ractapopulous
I guess this is inspired by the city of Ravenna in Italy and its stone walls.
Source Sentel