#Drupal: Changing fie icon

template.php

function themeName_file_icon($variables) {
  $file = $variables['file'];
  $icon_directory = $variables['icon_directory'];
 
  $mime = check_plain($file->filemime);
  if ($mime == 'application/vnd.ms-excel') {
    $icon_directory = path_to_theme() . '/images';
  }
  $icon_url = file_icon_url($file, $icon_directory);
  return '<img class="file-icon" alt="" title="' . $mime . '" src="' . $icon_url . '" />';
}