story identification - Can anyone identify this 90s teen-fantasy series, gems in backbone, big magic, evil king?

I've been trying to find this darn series of books for ages, I read them back in early 2001-02 and can't really remember much of them. I think there were 10-ish books, it was an easy read but a long series. On early publications, the covers, were mainly yellow, with small pictures of whatever happens in that book.

The book began with two siblings, a brother and a sister, running in a forest. She conjures up what can only be remembered as a golem type creature. He then uses a high magic 'blast' and wipes out the golem, knackering himself. His sister laughs at him for being 'powerful' but expending himself too much on one big magic blast. The beginning I remember vividly, the rest, not so much.

The story continues as a conflict happens, I believe two worlds are involved? The brother and sister are split up, but this is where my memory becomes vague.

The mechanics of the world seems that there are gems, or stones, set in the backbone, which in turn give access to magic. When the person uses them, they can draw too much, which ends up exhausting them. The 'big bad evil king' kills their father, and destroys their farm early on in the story.

Answer

You're definitely talking about is Chris Wooding's Broken Sky series.

Quite hard to find, I'm not sure if it's still in print. I also read it about 12 years ago, and remember the Golem fight well.

The story revolves around the journeys and trials of twins Ryushi and Kia. Forced to flee from their home during a violent and seemingly unprovoked attack by the forces of the King they adored, they are pressed to reconsider their naive world-view caused by their sheltered upbringing as they are caught up in events beyond their control and larger than either of them imagined. What starts with an underground resistance soon develops into a full-fledged rebellion against the tyrannical King Macaan and his equally malicious daughter Aurin, with Kia, Ryushi and all those close to them at the center of it all.

....

While the societies in Broken Sky rely on various infrastructures for their survival, such as water or Tusami City's magma-based geothermal power, one commodity which appears to rule many facets of daily life is the Spirit Stone. Extracted by mining as an inert, colourless gemstone, the Spirit Stones only take on their characteristic colour after being implanted by a Deliverer during a ritualistic ceremony called the pah'nu'kah.

During the ritual, the Spirit Stones are implanted along the spine - specifically, in the voids between their vertebrae - of a newborn child, being partially phased into their bodies so that only one hemisphere is visible. Once the ritual is complete, both the stones and the child forge a connection with the ley lines - conduits of raw energy running beneath the earth - giving the stones a specific colour and the child command over a certain ability later in life.