Sediment is a naturally occurring material that is broken down by weathering and erosion, and is transported by wind, water, ice, and then gravity which act on the particles.
A deep trough in the sea just off land is ideal for the formation as rivers and streams collect the sediment from the land and in time transfers this to the sea or ocean. Nature also helps as tides gather pebbles, rock and even volcanic ash and transfers this with the land sediment into these troughs. In time the pressure from above compresses the sediment and liquids are squeezed out leaving just the minerals themselves which form the rock.
There are many natural sea troughs in the world which form sea sediment but those off the USA, South America and India are ideal as the chart shows.
The rock formed is not a hard rock and easily worked for jewellery.
Some sea sediment is dyed and It is difficult to determine which, the only 100% way is to drill through the stone and see if the colour goes all the way through. If all the stone is a shade of one colour all over it could be dyed. Another option, which does no damage to the stone, is to see if the pattern and colours follow from front side and back.
The rainbow sea sediment is the prettiest as the colours are very eye catching and as this rock is not too hard good shapes can be formed.
Another form is Coral Jasper which looks like fossils within the stone.