Clear Round Rock...Please Identify

[venicegirl]

Hi, I found this clear round rock on a hike in Northern California. Is it a quartz? It cuts glass, so I'm thinking that it is. I'm not a rock hound, or at least, I wasn't until I found this pretty little thing.

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[teara]

It looks at tho it spent some time in the water. I find alot of quartz in the river here that look similar to it.