Rocks and Minerals

Rocks that contain a valuable mineral or metal that can be extracted are called "ore". A fairly common ore found in the monument is called chrysocolla. Most often, gray to red rock holds streaks of greenish blue chrysocolla, which gets its color from copper.

NPS photo

 

Geology in southern Arizona and the Sonoran Desert region is diverse. Some rock formations in the monument date back to 2 billion years ago, while the volcanic region southwest of the monument has young rock formations only hundreds of years old. The mineral rich soils were mined throughout the 1900’s, and for thousands of years before that, native people were utilizing stones for hunting, agriculture, construction, and art. Learn about some of the "rocks" you may find in the monument below.

Please remember: Organ Pipe Cactus National Monument preserves these beautiful resources for everyone to appreciate. Please leave these desert jewels where you found them, so that other visitors can continue to enjoy their beauty for years to come. Visit the NPS Geology website and the NPS Geodiversity Atlas to learn more about geology across the United States.

 

First Things First…

What’s the Difference Between a Mineral and a Rock?

The easy explanation: Just like baking, minerals are the ingredients (butter, sugar, vanilla, etc.) and a rock is what the ingredients make, like a cake or cinnamon roll!

A more in-depth explanation is that each pure mineral has only one thing that it is made of, and on a microscopic level, you would see the same repeating crystal. Rocks can be different shapes and sizes, from boulders to sand grains, and even the same types of rock may look different. On the microscopic level, you might notice several different kinds of minerals will make up a rock.

Types of Rocks

There are three types of rock: Igneous, metamorphic, and sedimentary. Each are made differently and have different properties.

Igneous Rock

Igneous rocks are formed when volcanic magma or lava cools. This usually happens without too much pressure, so igneous rocks are light and airy. Igneous rocks are the most common type of rock in the monument because this area was once covered with active volcanos! An example of an igneous rock here would be scoria—which is like pumice that you may have seen in stores.

Metamorphic Rock

Metamorphic rocks undergo intense pressure and heat when they are made deep within the Earth. Like mushing two colors of clay together in your palms, the clay warms up and becomes soft, and the colors swirl together, until they eventually mix completely. An example of a metamorphic rock in the monument is quartzite.

Sedimentary Rock

There is no high heat needed to create a sedimentary rock. Smaller rocks, gravel, and sand are “glued” together with smaller crystals. An example of a sedimentary rock in the monument would be the caliche or crust that makes up a lot of the hard ground.

What is an Ore?

An ore is any rock that contains a mineral or metal that can be extracted and refined, like steel that was originally held in an iron ore.

 

 

NPS photo

Chrysocolla

Chrysocolla (pronounced "krise-ah-cola") is a copper mineral with a striking cyan color that stands out against the desert landscape. It can have hues ranging from a seafoam green color to sky blue to teal, and because of its beauty has been used since antiquity as a gemstone for carving, and in silversmithing and goldsmithing. Chrysocolla can be a good signal that copper may be nearby, as it can be found in the oxidizing zone above copper deposits. Here at Organ Pipe Cactus, that means there’s a good chance of spotting some during a hike near the many historic mines found here in the monument!

 

NPS photo

Malachite

Did you see a brilliant green rock when you were near one of the copper mines here at Organ Pipe Cactus? Malachite (pronounced "mal-a-kite") is a copper mineral with hues ranging from a seafoam green color all the way to a dark green, and has been used for millennia as a gemstone, a pigment, and even sculptural material. Malachite can be a good signal that copper may be nearby, as it can be found in the oxidizing zone above copper deposits. Here at Organ Pipe Cactus, that means there’s a good chance of spotting some during a hike near the many historic mines found here in the monument!

 

NPS photo

Obsidian

Ever been enjoying the great outdoors and spotted some glassy, black rock? You may have spotted obsidian!
Obsidian is formed when magma cools quickly, and is therefore an igneous rock. Obsidian is often found near rhyolite, another common igneous rock which makes up the mountains of Organ Pipe Cactus National Monument. Obsidian is formed when lava extruded from a volcano cools quickly, creating a glassy rock with no crystals. It commonly comes in hues of black to dark brown but can be tan to green as well. Black and brown obsidian twisted together is called “mahogany obsidian”, and it can be spotted in the monument along the Estes Canyon trail.
This sharp, glassy rock has been traded and used since time immemorable all around the world for arrow and spearheads, knives, jewelry, plates, ornaments, mirrors, and it’s even being researched for creating scalpel blades! It’s a breathtaking sight to see when exploring the outdoors!

 

Wikimedia Commons/ Transpassive

Hematite

Seeing any deep red rocks around the Organ Pipe Cactus lately? The most important mineral in iron ore is an iron oxide compound called hematite, is found in a wide variety of soils and rocks and is one of the most common minerals on Earth. This amazing mineral has many uses, including as a pigment, as jewelry, gilding, a polishing compound, and even as radiation shielding for science and medical equipment!
Its name is derived from the Greek word for “blood”, yet it comes in colors from black to silver, brown to red, has various surfaces all the way from metallic to a dull, earthy exterior, and comes in almost any form. With so many variables in its appearance, how is one to know it’s hematite they’re examining? Simple! Drag it across a surface it will leave a trail of dust on; no matter its color, texture, or form, the trail will be an earthy red color if it’s Hematite! There is a way to expose this master of disguises here in the monument!

 

NNPS photo

Quartzite

If you see any bright white, pink, or grayish stones, you probably saw quartzite!

Quartzite is a hard metamorphic rock made up mostly of quartz, and maybe some hematite, which will give the rock a pink color. Quartzite is often found along mountains as they are pushed upward through the ground, dragging metamorphic rocks with them. Early miners of the area used quartz to find gold deposits, as they are often found together.

 

NPS photo

Rhyolite

Rhyolite is one of the most common rocks around the monument. Rhyolite is formed as magma is exposed to the surface and cools quickly. Silica is a mineral found in many rocks, but rhyolite holds the most silica out of its metamorphic relatives. Iron levels in the rock give it a rusty, dusty red color. Rhyolite is the all that is left from the ancient volcanoes that formed the mountains here in the monument.

 

Rijksmuseum

Pumice

Feet sore from all that hiking? Treat your feet with pumice, a “Jack of all trades” rock found around the monument. Pumice is a lightweight and light-colored rock found all throughout the world. This rock is created when a volcano violently erupts and extremely hot, highly pressurized rock is expelled from it. It quickly cools and depressurizes, releasing the gases contained inside (similar to opening your favorite can of cola!), creating a vesicular, or porous, texture in the rock.

Pumice is so lightweight that it floats in water, unlike it’s similar looking yet heavier and darker-colored cousin Scoria, which sinks. This versatile rock can be used for just about anything: construction material, water filtration, book making material, scrubbing tools, abrasives like pencil erasers and polishes, medicines, and most importantly for your tired feet: as pumice stones, to exfoliant and refresh your tired feet after a long day hiking. You’ll have to get your pedicure pumice elsewhere though: this all-purpose rock is for your viewing pleasure only here at the monument.