In day to day wear, a diamond will not scratch BUT diamonds will chip on the girdle where they are most vulnerable. So, generally speaking should not be worn when doing household chores and definitely not when doing gardening!
As diamonds are the hardest known substance to man and should not be worn whilst doing household chores, then it goes without saying that all other gemstones and metals that are softer than diamonds should not be worn either.
Diamonds will scratch other items and gems such as pearls or opal. Always keep jewellery in different compartments in your jewellery box to prevent from scratching.
Your jewellery should always be the LAST thing you add to your outfit before you walk out the door. Cosmetics, hairspray and perfume are just a few of the enemies to your jewellery. Oil and debris attracts dust and grit which coat the back of your stones and inside settings. Chemicals in hairsprays can damage the settings in your jewellery.
