These instructions use US crochet terms and standard abbreviations. I have used dk yarn and a 4 mm hook and scraps of 3 colours for each coaster.
1. With 1st colour chain 4 & join into a ring. Chain 3 (counts as 1st dc), work 11 more dc into ring. Fasten off.
2. With 2nd colour and working between the stitches and not into the top of the stitches; ch 5 (counts as 1 dc & 2 ch), *dc in next space, ch 2; rep from * 10 times more. Fasten off.
3. With 3rd colour and working in the chain spaces; ch 3(counts as 1 dc), 2 more dc in space, *3 dc in next space (3 dc cluster); rep from * 10 times more. Join into the top of ch 3 with a sl st.
4. Sl st over to between the 3 dc cluster.
5. *Ch 4, sl st into next space between 3 dc cluster. Rep from * 11 times more.
6. I quite like how they look at this point, and if you are using chunkier yarn these may be big enough to finish here should you wish. But if not; sl st into the next ch 4 space.
7. Ch1, sc, hdc, treble into middle dc of 3 dc cluster below (see pic below), hdc sc, *in next space (sc, hdc, trb into middle dc of 3 dc cluster below, hdc, sc), rep from * 10 times more. Sl st into ch 1. Fasten off.
Sooo quick to whip up – they would make great gifts, perhaps piled into sets of 4 and tied with some string/raffia and a pretty label.