VUGS - THE HOLE IN YOUR ROCK

While all geodes contain vugs, not all vugs are geodes. 

I've discovered that there can be a lot of confusion about the differences between geodes and vugs. According to Mindat.org, a vug is a cavity in a rock, usually lined with crystals of a different material composition than the enclosing rock.

Geodes, on the other hand, can form in any cavity, but the term is usually reserved for more or less rounded formations in igneous and sedimentary rocks, while the more general term “vug” is applied to cavities in fissures and veins.

VUGS YOU LOVE

  This is my very favorite vug.  It's only about two inches at it's longest point and the cavity is a bit over one inch deep,but it's full of character. When I hold it in hand, it mostly looks brown, but you get it near lights and it turns into a star. I think the green is olivine and the orange spears are wolfenite.

HOW DO YOU IDENTIFY A VUG?

According to Mindat.org, a vug is a cavity in a rock, usually lined with crystals of a different mineral composition than the enclosing rock.This fanciful vug is lined with crystals that appear to be quartz.  But as someone who is always trying to listen to the rocks,all I see is an angry swirl with some crystal linings. Not a happy vug at all.

YET DISTINCT FROM A GEODE

An open space in a rock is not necessarily a geode.  To be a geode, the open space in the matrix must have a shell-like outer layer with crystal growth geodes:

 Sometimes vugs aren't crystal-lined, but do contain crystals. Here you can see two red-brown garnet crystals and the outer edges of the original vug where they were formed.  The garnets are a beautiful color, but both have flaws in their formation. They do make a wonderful display piece though!

The shot below shows another face of the same rock with empty vugs shown. When I cut this, I REALLY hoped I'd find some more garnets, but sometimes a hole is only a hole.

 I was ready to call the openings in this rock vugs. When I sliced the rock, the spaces were full of loose dirt and were frankly, ugly. After I cleaned it up, photographed it, and enlarged it, I could see that there actually is a lining on the holes in the rocks. However, that crystal lining doesn't make it a geode because there's no encompassing outer layer, so a vug it is.

The thing that makes this picture interesting to me is that the vugs are shown here at several levels of development from the dark spaces that are somewhat friable to finished crystal-lined shapes.

 And, here's a slice of a real geode.Notice the strong perimeter  banding that makes it obvious that it is separate from the surrounding material.

In this case the geode slice shows inclusions at the 4 o'clock and 6 o'clock positions.











ROCK & GEM MAGAZINE FEATURE!

If you are a subscriber to Rock & Gem Magazine, don't miss my article in the January issue about Intarsia/Pietra Dura. It profiles the craft and the history of this artistic craft through the vision and accomplishments of renowned artist Naomi Morgan.

Thank you for visiting LapidaryWhisperer.com  I hope you enjoy my posts.I'd love to hear from you.

I wish all my readers the joy and blessings of the holiday season, however you celebrate it.

Your Lapidary Whisperer.

Donna Albrecht
donna@lapidarywhisperer.com