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Add code below to your theme into the file template.php and edit the name for the function "YOUR_THEME_NAME_breadcrumb". Clean cache on the site. Structure for breadcrumbs will become like here http://schema.org/BreadcrumbList. You can check structure here https://search.google.com/structured-data/testing-tool/u/0/

/**
 * Return a themed breadcrumb trail.
 *
 * @param $variables
 *   - title: An optional string to be used as a navigational heading to give
 *     context for breadcrumb links to screen-reader users.
 *   - title_attributes_array: Array of HTML attributes for the title. It is
 *     flattened into a string within the theme function.
 *   - breadcrumb: An array containing the breadcrumb links.
 * @return
 *   A string containing the breadcrumb output.
 */
function YOUR_THEME_NAME_breadcrumb($variables) {
  $breadcrumb = $variables['breadcrumb'];
  $output = '';
  $output = '<nav class="breadcrumb">';
  $output .= '<ol itemscope itemtype="http://schema.org/BreadcrumbList">';
  $count = 0;
  // We need to show url for each breadcrumb.
  $domain_path = !empty($GLOBALS['_domain']['path']) ? substr($GLOBALS['_domain']['path'], 0, -1) : $GLOBALS['base_url'];
  // add microdata to breadcrumb
  // @see http://schema.org/BreadcrumbList
  foreach ($breadcrumb as $key => $item) {
    $count++;

    preg_match('/<a.*?>(.*)<\/a>/', $item, $matches_name);
    $name = $matches_name[1] ?: '';

    if ($key < count($breadcrumb) - 1) {
      preg_match('/".*?(.*)"/', $item, $path_bc);
      $path = $path_bc[1] ?: '';
      $item = '<a itemprop="item" href="' . $domain_path . $path . '"><span itemprop="name">' . $name . '</span></a><meta itemprop="position" content=' . $count . ' />';
    }
    // For last item in breadcrumbs we need add info about it too.
    if ($key == count($breadcrumb) - 1) {
      $item = '<a itemprop="item" href="' . $domain_path . '/' . request_path() . '"><span itemprop="name">' . $item . '</span></a><meta itemprop="position" content=' . $count . ' />';
    }
    $output .= '<li itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem">';
    $output .= $item;
    if (count($breadcrumb) > $key + 1) {
      // Adds breadcrumbs separator.
      $output .= '>';
    }
    $output .= '</li>';
  }
  // Adds trailing separator.
  $output .= '';
  $output .= '</ol>';
  $output .= '</nav>';

  return $output;
}