Geology for Rockhounds

[1dave]

(Still Under construction)

MISSION: rather than give locations, Teach how to find locations.

With a little understanding on how our country was built and how to read Geology maps our hounding excursions can become more interesting and productive.

Here is a handy directory of LINKS to sections of specific interest:

Share your knowledge.
Books on Geology
Rock Stars - Brilliant Discovery's.
Identifying Rocks
Field Geologists
The Dying Times

Igneous

Diatremes
Hotspot Theory
Key to Finding Gemstones in Granite and Rhyolite
Flood Basalts - Hydraulic Earth
Mineral Belts
Pegmatites the Home of Gemstones
Where to Find Geodes
Mega-Thundereggs!
Delamination

Sedimentary

H2O-Simply complicated
D-Bone
Petrified Wood

Metamorphic

Garnets
Jade
Picasso Marble


Impact

Impact Craters
Impact Cratering Process


Utah's Western Neighbor, Australia!



What is in the area you are visiting? Here are a few quick tips:

Did you know garnets are magnetic? Ants can share a wealth of information.

Julie Powell and Sugar McDonald with magnets on rods, examining a Utah ant hill.



TIPS For Novices:
Tip #1. Check Ant hills! If there are crystals in the area you will usually find tiny bits on top of their hills. Quartz, Garnet, Peridot, . . .
Tip #2. Check stream beds! Bits of whatever is in the upstream watershed will be there. Follow the gold, petrified wood, or whatever upstream to it's source.
EXAMPLE: If you were south of Sacramento several hundred years ago, before all those people got in the way, in a dry season, imagine how easy it would have been to find where particular rocks were coming from.

Laguna Creek Watershed - south of Sacramento California

Tip #3. Knowing Where and When in Time to look is a great Luck Enhancer.



John McPhee wrote an interesting and informative series of books entitled:
Basin and Range, In Suspect Terrain, Rising From the Plains, Assembling California, and Crossing the Craton.
They have been compiled into a single and more complete book:
“Annals of the Former World.” A Great Read!

In short, Our world was formed by continents slamming into one another building mountains of basalt, andesite and granite; breaking apart in new sections, pinching sections between new collisions, and growing by scooping up islands as the continent sailed westward.



Throughout time we have been constantly bombarded by meteors, asteroids, comets, and even another planet which broke off our moon. Except for that collision, the others have added zones and ever higher layers of exotic materials.

Mountains have worn away, their debris filling valleys as new mountains formed, rivers, lakes, and oceans coming and going leaving tumbled stones and layers of sand, mud,limestone and dolomite.

The Times they are a changing!
A mere 144 million years ago there was a sea where the Mighty Rocky Mountains now stand.



Information gathered by thousands of geologists over hundreds of years are available to be downloaded from your State Geology Organization and at:
USGS.GOV
ngmdb.usgs.gov/ngmdb/ngmdb_home.html



USAMapViewAvailable-1.jpg


A closer examination reveals that many areas are still incomplete.

At present (2013-14)New mapping is continuing at the following locations : ngmdb.usgs.gov/MapProgress/MIP_home.html

New-Mapping.jpg

Most maps show geologic information in unique colors printed over topographic maps with side charts explaining what the colors mean. Often there are additional section maps - A-A, B-B etc. Included, sometimes with detailed descriptions of each layer. The following is from Map #I-1901 Richfield Utah Quad:

1-USGS-RichfieldQuad.JPG


1GeologyUtahChinleRichfield-2.JPG

Note from another Utah map:

1GeologyAgeSanRafaelSwell-1.JPG

Centuries of excellent information!

[rockpickerforever]

Thanks for posting that, Dave. Yes, lots of useful information and links! (Although I'm sure it may as well be Greek to many, lol!)

Us left-coasters have the youngest rocks, only 100 million years old! Jean

[1dave]

Ah, to be only 100 million years old again!

[1dave]

Added link at the top of the thread to "Hydraulic Earth" - my theory for Flood Basalts.



Started a thread on where to find Geodes.

[1dave]

The Dying Times is such a big subject it is taking far longer than I originally thought.

In the meantime, I'm contemplating a new subject: "Mother Nature's Rock Making Boogie Woogie."

It has to do with how time, heat, and gravity are continually sorting, separating, and mixing rocks.
I'm not quite sure how it will all go together.

As light surface rocks are subducted and melted, they expand and become lighter and more buoyant.
But, as they expand, the pressure increases and melting stops unless more heat is applied, where again pressure increases. When rocks above give way, the rocks expand and melting rapidly increases and the magma starts rapidly moving up, melting country rocks and changing the chemistry. Crystals form and drop out unless viscosity is so great they are dragged along. What an amazing world!

Density S.G.:
Water 1.0

Sedimentary & Metamorphic rocks
Coal 1.1 - 1.4 - If dragged deep enough, carbon becomes diamonds.
Limestone 2.3 - 2.7
Gypsum 2.3 - 2.8
Marble 2.4 - 2.7
Sandstone 2.2 - 2.8
Shale 2.4 - 2.8
Rock salt 2.5 - 2.6
Mica schist 2.5 - 2.9
Quartzite 2.6 - 2.8
Gneiss 2.6 - 2.9
Slate 2.7 - 2.8
Dolomite 2.8 - 2.9
Nephrite Jade 2.95 - 3.33 Ca2(Mg, Fe)5Si8O22(OH)2, belongs to the amphibole group, a silicate of calcium and magnesium.
Jadeite Jade 3.20 - 3.33 Na(Al; Fe )Si2O6, belongs to the pyroxene group, a silicate of sodium and aluminum.

Igneous Rocks
Rhyolite 2.4 - 2.6
Granite 2.6 - 2.7
Andesite 2.5 - 2.8
Diorite 2.8 - 3.0 white sodic plagioclase feldspar and black hornblende.
Basalt 2.8 - 3.0
Gabbro 2.7 - 3.3 Ocean Crust - a plagioclase that has a high calcium content. The other dark minerals may include amphibole, pyroxene and sometimes biotite, olivine, magnetite, ilmenite and apatite.
- - - - MOHO - - - - - -
Peridotite 3.1 - 3.4 Lithosphere

[rockjunquie]

I just have to say- This is a really, really great post!

[petrifiedwoodfarm]

Thanks for sharing Dave! I picked up the Roadside Geology book for Montana, which flows along your theory of know the land to understand where to figure where to locate what your after.

It does take some time to understand though if you have never visited the locations / areas. Google does assist, as does this site!!!

Keep up the good work. Thanks for helping this Newbie.

Michael

[1dave]

added Picasso Marble to the Links List at the first of this thread.

[iant]

Dave, you are 'The Knowledge!' I salute you!

[melhill1659]

I'm noticing this is a pretty old thread but I've gotten so much enjoyment from reading it I wanted to take time to say THANK YOU! I enjoy, as much as any rock licker, looking over Rockhounding site info. But I get excited really learning the "geology" of it all! I WANT TO DISCOVER NEW UNFOUND TERRITORY. I'm very fortunate in my husband an I travel a lot. I read all I can about the state, island, area of the country we are visiting and the geological maps I can find. So thank you again for this tread. We're Vancouver Island bound this spring Wish Me Luck.
Melissa

[amygdule]

Some more Historical Geology