Beach nr Pefki Island resort is a narrow sandy beach. The sea is a bit rocky as you first go in, but you will be fine if you wear a pair of jellies or similar.

Hello

I have never found it rocky, it has always been sandy, I suppose it depends which beach you go on. The long beach is pure sand.

if you can travel by car or moped, there is a lovely beach called argathi which is just north od lindos, we were told about it by a local, it is so sandy, and is a holder of a blue flag, there are 3 tavernas on the beach selling great greek food and the water sports are only 10 euros each to participate, the guy who runs them is lovely and will talk to you all day about anything you would like to ask him about rhodes, we loved it.

Hello

Is this the beach at Haraki

Agathi Beach can be found just off to the left as you drive in to Haraki. It is a lovely beach and as the previous message said, holds an EU blue flag.
Pefkos has a number of beaches in addition to the main beach. Kavos beach is at the northern end of the main one and very similar, sand and a little shingle with gently shelving access in to the water. To the south of the main beach you'll find St Thomas and Plakia beaches. Both a nice alternatives to the main beach and still just walking distance from the center of Pefkos.

we took a boat trip to Argathi beach (from Lindos....we were staying in pefkos).......was fabulous, stopping at argathi for two hours, then on to deserted beach for barbecue, then on the way back stopped off in navarone bay for swimming and diving off the boat. A great day out which i can thoroughly recommend.
Pefkos beach is very narrow, but long. Doesn't have any tavernas to speak of dotted along the beach, but up the side roads just off the beach there are plenty to be found. It's not shingly, or rocky as far as I recall.