Join us on our other sites!
  • Outspire
  • Hiking
  • Snowshoeing
    • Snowshoe FAQS
  • Bandelier
  • Geology
  • About Us & Santa Fe
    • About Santa Fe
    • Santa Fe Links
    • Outspire Blog
  • Rates&Reservations
    • Reservation form
    • Gift Certificates
  • Contact Us

Episode 14   The Underworld

3/7/2021

0 Comments

 
The same naturalists who assigned lava and ash to the god Vulcan recognized that these once deeply-buried granitic rocks belonged to the realm of a darker and more deeply-throned god, Pluto, the god of the underworld. Consequently they are grouped together as the plutonic rocks.

Unlike the volcanic rocks, the textures of plutonic rocks are uniformly crystalline. As we've noted, this is a function of their environment of cooling, insulated beneath miles of crust, under enormous confining pressures.

But like the volcanic rocks, the color and silica content of the plutonic rocks varies according to their mineral content.

Silicate minerals rich in iron and magnesium are typically dark in color. These are the minerals we labeled mafic. Plutonic rocks rich in mafic minerals are correspondingly dark, like this 
gabbro:
Picture
Silicate minerals lacking iron and magnesium are light in color and relatively high in silica. Plutonic rocks composed of these minerals are light-colored as well, although they nearly always have at least a sprinkling of mafic minerals to give a pleasant contrast, like this granite from the Sierra Nevada:
Picture
Much of the granite in the Southern Rocky Mountains is pink or orange in color. The principal mineral in all plutonic rocks is feldspar, an aluminum-rich silicate, and in the old continental core of North America, most feldspar is rich in the metallic element potassium. Potassium feldspar is pink.  
Picture
Of course nature admits all sorts of intermediate cases between the poles of gabbro and granite. Classification schemes for the plutonic rocks were not standardized until the 1970's, and even today there is a whiff of dissatisfaction with the choices and their names. Geologists are not about to give up their beloved old rock names - diorite, tonalite, monzonite, syenite - which are rich with historical overtones, and every attempt to rationalize the classification of these complex rocks just makes things worse.
0 Comments

Your comment will be posted after it is approved.


Leave a Reply.

    Outspire Blog | Inspiration from the Outdoors

    What we've been seeing around Santa Fe and northern New Mexico on our hikes.

    Archives

    March 2021
    February 2021
    April 2018
    March 2018
    February 2018
    September 2014
    July 2014
    May 2014
    March 2014
    February 2014
    January 2014
    December 2013
    September 2012
    April 2012
    January 2012
    September 2011
    August 2011
    May 2011
    February 2011
    January 2011

    Categories

    All
    Animals
    Birds
    Man & Nature
    New Mexico Geology
    News & Events
    Plants

    RSS Feed

    NetworkedBlogs
    Blog:
    Outspire Blog
    Topics:
    Nature, New Mexico Outdoors, Santa Fe Hiking
     
    Follow my blog
Outspire Hiking and Snowshoeing

Check our Facebook page to
see what's happening now!

Tours

Day Hikes
Special Tours
Snowshoeing

Santa Fe

About Santa Fe
Santa Fe Links

Outspire blog

Outspire

Contact Us
About Outspire
Rates & Reservations
Gift Certificates
  • TripAdvisor
#1  for Santa Fe Outdoor Activities
#1 for Santa Fe Tours
Guides are members of Santa Fe Professional Tour Guides LLC