cpt-pre-get-posts.php

function customize_cpt_archive_query( $query ) {

    if ( is_post_type_archive( 'gemstone' ) ) {
        $query->set( 'posts_per_page', -1 );
	$query->set( 'orderby', 'title' );
	$query->set( 'order', 'ASC' );
        return;
    }
}
add_action( 'pre_get_posts', 'customize_cpt_archive_query', 1 );