"Rock Hound's" Webquest
Mystery Rock 2

What kind of a rock is this?

Where Found?  |  Rock Formations?  |  Layers?  |  Smushed Together?  |  Geology Tests? | More Information

Where did I find this rock?

I did a lot of hiking in Wrangell St. Elias National Park and saw there were lots of dormant volcanoes.

Mt. Blackburn 16390 ft (4996 m)	Mt. Sanford 16237 ft (4949 m)
Mt. Drum 16390 ft (4996 m)	Mt. Wrangell 14163 ft (4317 m)

What rock formations are in the area where I found this rock?

I did a lot of hiking in Wrangell St. Elias National Park and discovered a lot of evidence that volcanoes were once active there.  Along the Skookum Volcano Trail, I explored lava flows and marveled at towers of layered lava rocks.

 

Lava Flows
Lava Flows  on the  Skookum Volcano Trail (Wrangell St. Elias N.P.)	Lava  poured from the Skookum Volcano about 2-3 million years ago.  This lava flowed slowly from many  vents and fissures.  As the lava flowed further downhill, it began to cool and eventually turned to a dark-colored rock.  Over time this rock was covered by layers of ash and soil.  Now, many years later, erosion has worn away the soil exposing these lava flows.  Here is Christina near lava flows.
Layers of Lava
Lava Vents on the  Skookum Volcano Trail (Wrangell St. Elias N.P.)	2-3 million years ago, lava flowed from the Skookum Volcano.  This initial lava cooled and formed rock.  Later, more lava flowed over the already cooled rock.  This happened over and over forming layers of igneous rock.  Wind and glacial erosion later shaped this igneous rock into the interesting shapes we see today.

Did my rock sample come in layers?

Sedimentary rocks often form in layers as seen in much of my hiking in the Gates of the Artic National Park.  The rocks that I am trying to identify are not formed in layers.

My Rock Does Not Have Any  Layers Like the Rock in the Picture Above.

Does my rock sample look like a bunch of rocks smushed together?

Conglomerate rocks form by rocks pressing together to form a new type of rock as seen in much of my hiking in the Denali National Park.  The rocks that I am trying to identify are not formed by having many pieces smushed together.

My Rock is Not Smushed Together Like the One in this Picture

 

How would a geologist test this rock?

Tests	What to do	What I found out about  Mystery Rock #2
General Description	What is the grain size and texture of your rock?  Are there flecks of shiny material?	The grain size is very small,  the texture is very rough with many crater like holes in the surface, and there are a few flecks of white, sand-like  material embedded in the rock.
Color	Look at the sample and determine its color - white, black, green, clear, etc	The rock is brown with some shades of darker brown and a few light flecks.
Luster	Look at the sample to determine if the mineral is metallic in appearance (looks like a chunk of metal) or non-metallic (doesn't look like a chunk of metal).	There are no shiny flecks.
Hardness	Scratch the unknown rock with a known hardness to determine which is harder. Continue doing this with harder or softer minerals from the kit until the hardness is determined.	The sample can be scratched by pressing down hard with a knife so I would say it's hardness is around 5 on the Mohs hardness scale.
Streak	Rub your rock across  a piece of  tile (unglazed side) and determine the color of the powder. .	The sample makes a brown streak.
Fracture	Examine the mineral for areas where the mineral is broken. Is the break irregular or smooth?	Where the rock was broken, it has many indentations and parts sticking out.  The fracture was irregular.

 

First, I made an educated guess at what type of rock this was.  Then, I compared the data I collected on this rock to information that I found in National Audubon Society Field Guide to North American Rocks and Minerals.  If I identified the rock sample correctly, I made an identification card.  If I felt that was not the correct identification, I went back and reviewed my data and made another educated guess.

	Basalt g
	Color	Luster	Hardness	Streak	Fracture
	Brown	No Shiny Materials	5	Brown	Irregular
Submitting "Rock Hound":  Matthew Durant  Boston, MA

I want to learn more about igneous rocks

How Igneous Rock Is Formed  Good description of how igneous rocks are formed.  The site offers several examples of igneous rocks.

Igneous Rocks  Excellent descriptions on how igneous rocks are formed.

Intrusive Igneous Rocks  Great images and descriptions of igneous rocks that are formed intrusively.

Igneous rocks  Great images of igneous rocks.

Kinds of Volcanoes   Great images of the different types of volcanoes.

Volcanoes  A great description of how a volcano works.

Ask-A-Geologist  Ask-A-Geologist questions are answered by USGS employees, retirees, and contractors who have volunteered to participate in the project.

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