Atmos comes bundled with 1500+ material design icons which are available from https://materialdesignicons.com.
To use the icons include the following css file
<link rel="stylesheet" type="text/css" href="assets/fonts/materialdesignicons/materialdesignicons.min.css">
we have used material icons as default icon family in atlas. you can change the icons used in atlas by changing values in variables
//Icons$icon-font: 'Material Design Icons';​//Icon Mappings$icon-chevron-down: "\F140";$icon-chevron-up: "\F143";$icon-chevron-left: "\F141";$icon-chevron-right: "\F142";$icon-sidebar-pin: "\F930";$icon-sidebar-pin-off: "\F92F";$icon-search: "\F349";$icon-arrow-right: "\F054";$icon-arrow-left: "\F04D";$icon-close: "\F156";$icon-close-circle: "\F15a";$icon-check: "\F12c";$icon-check-circle: "\F5e0";$icon-circle: "\F130";$icon-fullscreen: "\F293";$icon-fullscreen-close: "\F294";$icon-reload: "\F453";$icon-menu: "\F35C";