FMF - Friends of Minerals Forum, discussion and message board

[novicetumbler]

I look at this and I can only assume that during formation some impurity like sand or something got into it and got extruded during cooling, forming these fibrous 'strands.'

I can tell you all day about how plants grow but I couldn't tell you how this stuff forms! Curiosity bites me and makes me ask!

[gemlover]

Rutile crystals in quartz. As the melt cools, the elements forming the rutile (titanium dioxide) crystalize at a higher temperature than the pure silicon dioxide (quartz).

[novicetumbler]

Thank you, my curiosity is satisfied!

[John S. White]

The explanation could be a bit clearer, I feel. It implies that the quartz is derived from a melt and that is not the case. What has occurred here is the growth of rutile needles (rutile is titanium dioxide) which were attached at the base to a matrix. They no doubt grew from a vapor phase. Following the growth of rutile, quartz crystals began to grow around the rutile and in this instance completely encased them. The piece has subsequently been shaped and polished by a lapidary. This piece appears to have come from Brazil where there are several localities that have produced many thousands of similar specimens, some of which are just rutile without quartz having grown over it.