It’s called “Shell Stitch” or “Shell on Shell” or “Solid Shell” or what ever you happen to call it. No matter the name, it's one of my favorite crochet stitch patterns and I use it a lot when designing projects.
As the name Solid Shell indicates, it is solid, not lacy, but has a light look and lovely texture. Fabric made from a lighter yarn, such as sport or fingering weights, in this pattern drapes beautifully.
Another reason I like it is simplicity. Only three stitches, chain, single and double crochet, make the entire pattern. The rows alternate in a half drop pattern so, once established, it’s easily memorized. Shaping in solid shell is straight forward as well. The shells are easily adjusted for half shells when decreasing or added stitches when increasing.
Another of its wonderful properties is the ability to tame variegated yarns. Variegated yarns can have some disturbing color effects in the most unexpected ways. They are lovely in the skein but can become “jittery” or “clumpy” or just plain unattractive when worked into fabric. I’ve had success with the solid shell pattern with several variegated yarns.
Try this pattern. Here are the written directions and the chart. Start with some leftover yarn and make a pillow or throw. See what happens and have fun.
Multiple of 6 + 1 (add 1 for beginning chain)
1st Row: 1 sc into 2nd ch from hook, *skip 2 ch, 5 dc into next ch, skip 2 ch, 1 sc into next ch; repeat from * to end, turn.
2nd Row: 3 ch (counts as 1 dc), 2 dc into first stitch, *skip 2 dc, 1 sc into next dc, skip 2 dc, 5 dc into next sc; repeat from * ending last repeat with 3 dc into last sc, skip turning ch, turn.
3rd Row: 1 ch, 1sc into first stitch, *skip 2 dc, 5 dc into next sc, skip 2 dc, 1 sc into dc; repeat from * ending last repeat with 1 sc into top of turning chain, turn.
Repeat rows 2 and 3 for pattern.