That's way too much though.....5 gold or platinum coins weighs 1/10th of a pound in D&D. Gold and platinum are rather heavy elements. 5 coins is not going to be the same weight as a tiny piece of jewelry, like a ring or earring, or a precious stone/gem.
In general, just don't worry about it. Maybe assume that precious stones and gems are something like half the weight of a coin, if you need to guess (even though some will be heavier and some may be lighter). Jewelry, just mentally picture it alongside a stack of coins and guesstimate how many coins would be roughly the same size, and use that as a rough estimate of weight.
Like, maybe a typical expensive necklace would weight 1 pound or so, while a cheap one might weigh 1/10th or 1/5th of a pound from having only one precious stone on it and no metal chain. With a metal chain, it might be 1 pound or so, I dunno.
For bigger jewelry and art, just guesstimate based on a similarly-sized item. A big painting? Well, maybe it's the same weight as a few yards of canvas, since it's got a wooden frame and such too. A statuette or bust the size of your head? Maybe it's the same weight as a battleaxe or a spool of rope or a full jug of ale. A golden crown studded with gems and precious stones? Maybe it's the same weight as a battleaxe too, since gold is heavy.