• Rainbow over Half Dome

    Yosemite

    National Park California

Sculpture? Jewelry? Pegmatite?_081128

September 07, 2013 Posted by: JL - Park Ranger (White Wolf)
Sometimes the planet Earth seems like an inventor constantly coming up with new ideas. On a walk near White Wolf earlier this season, I was surprised to find a jammed-together patch of milk-white rocks almost two feet long; geologists call this pegmatite, and define it as a very coarse-grained igneous rock. The names that we give to rocks are often simply ways to refer to their stories; "igneous" refers to any rock solidified out of molten rock, and "coarse-grained," besides referring to the rock's appearance, indicates that the crystals of which it is composed cooled exceptionally slowly and so had time to grow very large. (The dried lodgepole pine needles on the right-hand side of the photo are approximately two inches long.) The crystals of this rock are predominantly of the mineral feldspar, which gives it its milky-white color. I like to think of a pegmatite as a rock which has had a long time to think.

Pegmatite near White Wolf

To stumble upon this rock while hiking around the White Wolf area is to feel that you have discovered some lost piece of jewelry, an ivory-colored artwork that was tossed into your path just moments before. Yet it has taken at least 80 million years for this pegmatite to arrive in this place in this form. It began its life as molten rock on the inside of a volcano; eventually it cooled, and the rocks above it were worn away by rain, snow and ice. More recently, this rock and the Sierra Nevada as a whole were lifted up over the last ten million years by forces not completely understood. All of these events together have resulted in this jagged, bone-white sculpture lying in the Sierra sun on a summer afternoon. It is not exactly a "new" idea, then, but is nevertheless a beautiful testimony to the creative powers of the planet on which we live.
 

White Wolf, Water-Rock-Wind, JL




2 Comments Comments Icon

  1. Jeff - Santa Maria, CA
    August 06, 2014 at 10:40

    This is a beautifully written article. Thanks for sharing your discovery.

  2. Edie - Yosemite, CA
    September 12, 2013 at 08:40

    The link on the main Yosemite Ranger Notes page to this article actually is recursive. It just takes you right back to the main page instead of this one. I got here by figuring out the article URL format, substituting /Sculpture-Jewelry-Pegmatite.htm for /rangernotes.htm Also, RSS articles link to: http://www.nps.gov/index.htm instead of the actual articles. HTH, HAND. Edie

 

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Did You Know?

Yosemite Museum

When it opened to the public on May 29, 1926, the Yosemite Museum became the first museum building in the national park system, and its educational objectives served as a model for parks nationwide. It still functions much as it was originally intended, and currently exhibits items which mainly reflect the Native occupation of Yosemite Valley and its surroundings. When in the park, you can visit with one of three cultural demonstrators who primarily staff the Museum.