Airlines generally accept no liability for such items.
AA, for example, excludes "fragile items". For domestic travel, they also state:
"No liability for photographic equipment, computers, VCRs and any other electronic equipment including software or components, jewelry, cash, documents, furs, works of art or other similar valuable items
Other items that are not covered in our limit of liability include, but are not limited to: antiques, books, china, fragile items, liquids, medicines, perishable items, securities and negotiable papers or silverware
And for international travel, the limit is $9.07 per pound.