The following are some ideas to consider in writing an essay that describes an object, in this case, a necklace:

• Size: How long is the chain? How large is the heart pendant? You might want to use some numbers here (like the chain is 18 inches long), or you might want to use adjectives. If the heart is rather large, you might describe it as enormous, grand, or massive. If it is small, you might describe it as teeny or miniscule. Also consider the thickness of the chain. Is it dainty (and thin) or is it wide?
• The color: You mention that it's gold, but you could add details here. Is it a flat gold? Or is it more of a sparkling gold?
• The weight: When you hold the necklace in your hand, how heavy is it? Do you think it feels substantial, or is it nearly weightless?
• The details: Does the necklace have a clasp? Does the heart have an inscription or any other writing? Does the heart open like a locket? Are there any other jewels on the heart? Does it sit straight on the chain, or is it tilted slightly to the side?
• Touch: How does the heart pendant feel? Is it smooth, or does it feel bumpy? Does the bottom of the heart have a sharp corner?

Once you combine all of these details, you might end up with a paragraph that looks something like the following:

The chain, which is round and 20 inches long, looks like a thick rope. A teeny heart dangles from the chain, its sharp corner sitting slightly off-center. On the back of the heart are the initials BTA, which is my monogram, etched in a curly font. A sparkling aqua gemstone sits at the top of the heart, adding colorful radiance to the gold heart. A miniscule lobster claw clasp joins the two ends of the rope chain, slightly smaller in diameter than the chain. The gold heart pendant is nearly weightless, a dainty addition to the shiny chain.