Looking for a youth adult (I think) fantasy series I read in the 90's with broken crystal power shards

Not sure when the books were released, but I read them probably in 93-95 era. There were multiple protagonists in this series and viewpoints jumped around. I believe there was time travel involved and that some of the characters were from different times and the times got blurred at points. Each shard of this crystal imbued more powers that were kind of.... telepathic in nature and characters good and bad were trying to gather multiple shards. I believe (this could be wrong) that mentally speaking with wolves and getting their help was one thing that the protagonists did. There was a series of caves being explored as well with shards being scattered across time.... I'm sorry if this is really vague, it's been so long it is very fuzzy!. Thanks anyone who has any ideas!