Garret Romaine - Rocks, Gems, and Minerals of the Rocky Mountains

Rocks, Gems, and Minerals of the Rocky Mountains

Garret Romaine

Copyright 2014 Morris Book Publishing, LLC

ALL RIGHTS RESERVED. No part of this book may be reproduced or transmitted in any form by any means, electronic or mechanical, including photocopying and recording, or by any information storage and retrieval system, except as may be expressly permitted in writing from the publisher. Requests for permission should be addressed to Globe Pequot Press, Attn: Rights and Permissions Department, PO Box 480, Guilford CT 06437.

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Falcon, FalconGuides, and Outfit Your Mind are registered trademarks of Morris Book Publishing, LLC.

Photos by Garret Romaine unless noted otherwise.

Acquisitions editor: David Legere

Project editor: Alexandra Singer

Text design: Sheryl P. Kober

Layout: Sue Murray

Library of Congress Cataloging-in-Publication Data is available on file.

ISBN 978-0-7627-8475-2

The author and Globe Pequot Press assume no liability for accidents happening to, or injuries sustained by, readers who engage in the activities described in this book.

To my son Nelson, may he keep finding what hes looking for...

Contents

Acknowledgments

Special thanks to the museums that assisted me with this book.

Jim McReynolds, executive director of the Wallace Mining Museum in Wallace, Idaho, supplied several raw ore specimens from his excellent collection. His museum is a must-see when in Idahos famed Silver Valley.

Ren Payne, image archivist at the Denver Museum of Nature and Science, patiently allowed me to browse her online image catalog and work through permission issues.

Dr. Lara ODwyer-Brown, curator of the Rice Northwest Museum of Rocks and Minerals in Hillsboro, Oregon, was always willing to rummage through her collection for another obscure sample.

Also, thanks to Rachel Houghton, veteran technical communicator and longtime friend from Portland, Oregon, who helped with photography, touch-up, editing, and encouragement, and to Martin Schippers, Frank Higgins, and Dirk Williams, who assisted in the field.

Rice Northwest Museum of Rocks and Minerals, ricenorthwestmuseum.org

Overview

About Geology

The term geology is a combination of two Greek expressions: Geo refers to the earth, and logos refers to the logic and language used to explain your observations. So think of geology as a way to organize and explain the earth processes that we see all around us. For some of the strange shapes we see, an educated explanation would be great. Most of what we know is good guesswork, based on lab experiments and inferences that take many detailed drawings to explain and a lifetime to understand. Fortunately, the more you see, the better things fall into place.

Geology is a young science, dating to 1815 if you start with William Smiths first geology map. But geology actually begins much earlier. Long ago ancient Greeks such as Pliny the Elder described various rocks and minerals, and many other scholars documented the metal mines of the times. Later, some of the smartest and most educated scientists laid down the basics, such as Nicolas Steno (163886), who observed that, most of the time, the rocks at the bottom of a cliff are older than the rocks at the top. He called that the Law of Superposition, and it helped explain how fossil seashells ended up on mountaintops. He also developed the Principle of Original Horizontality, which states that sedimentary rocks are usually deposited flat, although there can be local pinching, advancing, and other variations. Later, James Hutton presented Theory of the Earth in 1785, and Sir Charles Lyell wrote Principles of Geology in 1830. Arguments soon arose over the question of whether geology happened in slow, methodical processes or in short, catastrophic bursts. Once these distinguished thinkers realized the great age of Earth had nothing to do with Biblical teachings, they knew the answer was actually both.

There are two key points to consider when trying to understand geology: time and entropy.

• Time. The earth is a very young planet and thus still very active. But its also very old. Even though scientists have measured the earth at 4.6 billion years old, thats young in the context of a 20-billion-year-old universe. Given enough time, a lot can happen on a young, geologically active planet. We have earthquakes, volcanoes, and moving continents. The forces that boil up from the earths magnetic core are a long way from burning out, and they are relentless. Some activities happen quickly, like tsunamis, and we have the video. Other forces take millions of years, leaving clues like all the mica flakes lined up in a schist. Good field observers can identify the obvious signs of things that seemed to happen before and apply those signs to the present and future.
• Entropy. Things fall apart all the time. Stuff happens. Storms rearrange coastlines and rework river channels. Earthquakes, volcanoes, windstorms, and floods all move mountains and leave scars that heal. A rock balanced precariously atop another rock will not remain for long; eventually, it will shake loose. The earth is very efficient at recycling all that surface mayhem, hiding many clues. Mountains rise, then get ground down under glaciers and unrelenting rain. Tight chemical bonds that hold atoms together eventually weaken thanks to water, heat, pressure, and time. Oxygen in the air constantly rusts iron and dissolves minerals. Those forces are always at work and are easy to predict but hard to imagine sometimes. Try to picture the Yellowstone River under flooding conditions that happen once every 100,000 years. Thats mayhem on a continental scale. Now imagine the resulting gravel bars as the river recedes from flood stage, and think about the possibility of being the first rockhound to check for Dryhead agate on those newly stirred gravels.

Given enough time, almost anything can happen, and it usually does. We rarely see these processes at the surface, and we can only imagine what takes place at great depths. Thats where the logic comes in. There is a lot of math, chemistry, physics, biology, and just general science involved in sorting out whats going on in the field. But youre mostly interested in what you can see and collect, so read on.

Rocky Mountain National Park, north-central Colorado

Photo courtesy of Bob Fanshier

Think in Series

We dont get many absolutes in nature, so numbers, such as percentages of minerals present, help when thinking about crystal compositions. Just as there are probably no two snowflakes that are exactly alike, most granites differ in some way. Some basalts may have more iron and magnesium present, and some may have more feldspar. Some may have more magnesium and some more iron. You cant exactly tell without expensive equipment. And usually it doesnt really matter to that many decimals if you have a rough idea. You just want to collect the interesting forms, and you dont need a PhD in structural geology to dig out a seam of agate. You do need a hard hat, however.