It looks like a polished stone surface to me. Download it for free, as always.
Source V. Hartikainen
Prismatic Abstract Line Art Pattern Background 2
Source GDJ
Here's a camo print with more tan and less green, such as might be used in a desert scenario. This is tileable, so it can be used as a wallpaper or background.
Source Eady
Super detailed 16×16 tile that forms a beautiful pattern of straws.
Source Pavel
A background formed from an image of an old tile on the New York Metropolitan Museum of Art website. To get the base tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
From a drawing in 'The Quiver of Love', Walter Crane, 1876
Source Firkin
You know you can’t get enough of these linen-fabric-y patterns.
Source James Basoo
This one could be the shirt of a golf player. Angled lines in different thicknesses.
Source Olivier Pineda
ZeroCC tileable beechwood wood texture, generated in Neo Texture Edit by me. CC0
Source Sojan Janso
Spice up your next school project with this icon background.
Source Swetha
The following free background pattern has glossy diagonal stripes as a texture to it, and it's colored in a light blue gray color. This background pattern is suitable for using in web design or any other graphic design projects. This applies to all background patterns here.
Source V. Hartikainen
This texture looks like old leather. It should look great as a background on web pages.
Source V. Hartikainen
Has nothing to do with toast, but it’s nice and subtle.
Source Pippin Lee
Awesome name, great pattern. Who does not love space?
Source Nick Batchelor
Seamless Prismatic Geometric Pattern With Background
Source GDJ
From a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.
Source Firkin
Dark, lines, noise, tactile. You get the drift.
Source Anatoli Nicolae
Sharp but soft triangles in light shades of gray.
Source Pixeden
This was formed by distorting an image of a background on Pixabay.
Source Firkin
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
A seamless gray background texture suitable for use on websites. To me, it has the look of stone. Feel free to modify it to meet your needs (by making it a bit lighter or darker, for example).
Source V. Hartikainen
Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
This background image has seamless texture that resembles a surface of gray stone.
Source V. Hartikainen