Sass does not currently support mappings. You'll have to live with lists of lists for now.
$icons: star "\2605", lightning "\26A1";
@each $icon in $icons {
$key: nth($icon, 1);
$value: nth($icon, 2);
.icon-#{$key} {
@extend .icon;
&:after {
content: $value;
}
}
}