Saturday, August 22, 2015

Field Trip: Laytonville Quarry, Laytonville, Mendocino County, California


Quarry, as seen from parking area
The Laytonville Quarry, also called Longvale Quarry, is famous among rock hunters and geologists, for being the Type Locality (original discovery site) of the three minerals Deerite, Howieite, and Zussmanite.  (Side note: these three minerals were discovered in 1965, and named after the authors of this book: Introduction to the Rock-Forming Minerals)

Difficulty of access: Near highway, trail is easy, but you need to be able to do the 50-foot sprint across a four-lane highway very quickly.
Trail is difficult to spot, but it's to the left of the sign, near the big rock
Materials Found: Rare minerals Deerite, Howieite, and Zussmanite, as well as small but well-formed pyrite cubes, and masses of small garnets.
Howieite (black crystals)

Equipment Needed: Hiking boots, water bottle, rock pick, safety glasses, sun hat, backpack for carrying specimens.

Safety Issues: Site is somewhat remote and gets extremely hot in the summer. Beware of heat exhaustion, take plenty of water and cool off in the shade when you can. Rattlesnakes are an issue, as are black widow spiders -- be careful of where you put you hands and feet, and wear boots that protect your ankles. Dead grass and loose rocks make steeper portions of the path extremely slippery.

Directions: Site is approximately 17.5 miles North of Willits on Highway 101. You will see a large pullout on the left side of the road -- this is the parking area (It's generally safest to proceed up the road a ways to find a spot to turn around before attempting this).
Garnets
If you'd like a list of other minerals found at this site, check here.
And if you'd like to do further reading on the subject, I recommend: Geology of the Covelo/Laytonville Area.

Good luck and happy hunting!

Saturday, July 18, 2015

Understanding Fossilization




Fish fossil, Jalama Beach, California


Fossilization is a topic that is often poorly understood among the rockhounding community. At nearly every club meeting or field trip, there is always somebody picking up a random rock with quartz veins running through it, and insisting it is a fossilized animal of some sort. Or finding concretions and wondering if they are petrified dinosaur eggs.

I hope that by reading this, you will come away with a better idea of just what fossils are, where to look for them, and how to identify if you have actually found something special.

What is a fossil, exactly?
A fossil refers to the remnants of living organisms which have been preserved in the form of stone. Usually, it refers to the preserved organism itself, though it can also be applied to traces left behind, such as fossilized footprints, burrows, or coprolites.


Geologic environments
Fossils are found in sedimentary rocks. Ancient seafloor deposits, sandstone, mudstone, limestone, or volcanic ash deposits -- this is where you want to search. Very VERY rarely, a fossil will be found in metamorphic stone, but only if that stone was originally sedimentary to start with. Usually, when rocks metamorphize, any fossils contained will be so deformed as to be unrecognizable, but occasionally one will retain enough shape to still be identified as such.

You will never find fossils in igneous rocks. [Volcanic ash deposits are considered sedimentary].


Types of fossilization

So how do fossils form? Well, that depends a bit on exactly what type of fossilization has occurred. 

  • Petrifaction: The original material is slowly replaced by minerals which gradually seep in from the surrounding matrix. The majority of fossil bones and petrified wood are preserved in this manner.
  • Molds: These occur when the remains of the organism decays or dissolves away, leaving only an empty cavity in the rock. These can retain a surprising amount of surface detail imprinted on the rock.
  • Casts: These are when a mold becomes filled with a mineral such as pyrite, calcite, or agate, which takes the form of the mold.
  • Steinkerns: The interior of a shell becomes filled with mud, which hardens, and eventually becomes free of the matrix. Basically, a cast of the inside of a shell.
  • Trace Fossils: These are not fossils of the organism itself, but rather some trace of it -- preserved footprints in mud, for example, or nests/burrows, etc.


How to tell if it's a fossil
Does it have clearly identifiable bones/teeth/wood grain/shells? Always remember that hard parts are MUCH more common than soft part fossils. If you think you've found a tooth, you're more likely right than if you think you found a petrified eyeball.

The fossilization process has to race against decomposition. And fossil-forming can be a very long process, sometimes taking thousands of years. The harder and more rot-resistant parts of the organism are what is likely to actually be left, by the time fossilization has fully set in.

Be sure to take a look at the type of rock you found it in, and the geologic setting nearby. Is it sedimentary? Are there other types of fossils found in the area?

And if you pick it up and have to wonder, "Is this a fossil?" instead of immediately going "Wow, a fossil clam!" ....then it may not be a very good specimen anyway!

If you'd like to learn more about fossils and how to identify them, I highly recommend the following books:

National Audubon Society Field Guide to North American Fossils


Smithsonian Handbooks: Fossils

Happy hunting!

Monday, March 23, 2015

Have a location you want featured? Let me know!

Dear readers,

I've gotten a few suggestions lately about spots to cover for this blog. Do you have a location you would like to see written up here? It doesn't have to be a major spot, I'm willing to visit smaller and more out of the way sites as well.

Suggestions accepted in the comments, or you can send me an email.

I'm looking for sites located only on public land, for ease of access.

I'll take suggestions for anywhere in the whole wide world, but the chances of my actually visiting the place are vastly higher if it's in Sonoma, Lake, or Mendocino Counties, or somewhere nearish those.

Looking forward to your suggestions!

Saturday, December 27, 2014

Field Trip: Lake Mendocino, Ukiah, California

Lake Mendocino is a fun place to wander around and look for rocks, though you have to know the areas of shoreline that are best in order to find much. We've previously covered the area where the Russian River enters the lake, but today we'll have a look at the opposite end. It's definitely best to go when the water isn't too high.

From Ukiah, take State Street north to Lake Mendocino Drive, and park in the parking area by the dam. Walk all the way across the dam, until the paved path leaves the lake and begins to go up the hill -- at this point, take the small trail to the left that takes you down to the shore.



You're aiming for the point of land that sticks out into the lake, with a sheer dirt cliff. As you approach, start inspecting the cobbles around your feet for colorful jaspers.


They come in various colors, from purple and yellow to bright reds. They're not very concentrated, but definitely worth it when you find one!


You should also watch for petrified wood -- it is rare, but interesting. The wood grain is well-preserved, and some pieces even have bits of charcoal embedded in the stone.

Lake Mendocino Petrified Wood
And, of course, don't forget to admire the lovely views of the lake and the mountains while you're there! If you're lucky, you might spot some great blue herons, or even a bald eagle or two.


Happy hunting!

Sunday, September 14, 2014

Mineral of the Day: Fluorite




Fluorite is a popular mineral for collectors, since it is relatively common and inexpensive, and can be found in large, showy crystals of many shades and colors.

Frequently cubic-shaped, and blue, purple, green or yellows [though it can be found in every color of the rainbow, less commonly]. It is frequently found alongside minerals such as calcite, dolomite, galena, and sphalerite.

Some fluorite will fluoresce beautifully under UV light [as the name might suggest].

Some fluorite will even fluoresce in sunlight!

Care should be taken to keep specimens stored out of direct sunlight, as the color may fade, and it should not be stored in water, as this may also damage the specimen.