Correction in the Coddington magnifier is achieved through the use of a single thick lens with a central groove diaphragm. This provides for sharp, crisp images.A problem sometimes encountered in using a high power magnifier is the lack of sufficient light on the object. A bulb inserted in the groove of the Coddington lens illuminates the object being examined eliminating this problem. Requires two AA batteries (not included).
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"Invaluable to rockhounds of all ages."--Science Teacher.
"One of the 100 outstanding Sci-Tech books of the year."--Library Journal.
"Anyone interested in minerals and gems will want a copy of this beautifully-illustrated book."--Science Books & Films. (all in color)
Derived from the world-renowned McGraw-Hill Dictionary of Scientific and
Technical Terms, Sixth Edition, this vital reference offers a wealth
of essential information in a portable, convenient, quick-find format. Whether
you're a professional, a student, a writer, or a general reader with an interest
in science, there is no better or more authoritative way to stay up-to-speed
with the current language of geology and mineralogy or gain an understanding
of its key ideas and concepts.
Written in clear, simple language understandable to the general reader, yet
in-depth enough for scientists, educators, and advanced students, The McGraw-Hill
Dictionary of Geology & Mineralogy, Second Edition:
The Mineral Hardness Ruler is a stimulating visual aid, educates in one phase of mineralogy, and provides the standard ruler measurement scales needed in classes.
Rockhounds, mineral enthusiasts, students, teachers, geologists, and any one interested in rocks and minerals will find the Mineral Hardness Ruler a handy visual aid for quick information on mineral hardness.
The two-sided, flexible, glossy, vinyl ruler consists of five scales: three measurement scales and two mineral hardness scales. The measurement scales are in standard ruler measurements of tenths of inches, sixteenths of inches, and millimeters. Mohs' relative hardness numbers are integrated into the inch scales, while a separate scale exists for an absolute mineral hardness scale by Rosiwal.
On one side of the ruler are pictures of the ten common minerals, in full color, selected by Mohs for his relative hardness scale. On the reverse side of the ruler are six common items with their relative hardnesses. These items, along with known minerals, can be used as a handy field kit to test the relative hardness of an unknown mineral.
Hardness is one property of a mineral that can be used to distinguish among similar minerals. A given mineral can scratch any other mineral of the same or softer hardness. Over a hundred years ago, the German mineralogist Frederick Mohs devised the relative hardness scale that has found favor with mineralogists for over a century. Others, such as Rosiwal, formed absolute hardness scales using the same minerals as Mohs. For example, diamond, the hardest substance in Nature is not twice as hard as apatite, 10 versus 5, but over twenty thousand times as hard, 140,000 versus 6.5.
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