A tribute to the Year of Crystallography - Haüy´s Models

"It would be good if the readers, who wish to follow the details of these demonstrations, make themselves or have made, in cardboard or any other materials, solids that represent the principal varieties of crystals"
Haüy, 1784 - Portrait of French naturalist Haüy with contact goniometer, an instrument to measure the crystal angles. Haüy refused to use any other type of gioniometer during his lifetime, even if after 1809 high-accuracy optical goniometers, using reflection of light to measure the angles, were introduced.

The Danish anatomist and naturalist Nicolas Steno (1638-1686) was the first to note in 1669 that the faces of a crystal (2014 was also dedicated to the science of crystals) are always arranged in specific angles and crystals display a characteristic symmetry. Mineralogist René-Just Haüy (1743-1822) used a mechanical or contact goniometer to accurate measure the angles between the faces, realizing that all the various shapes of crystals could be reduced to just a limited number of basic geometrical shapes. In 1784 he published his observations in the book" Eassai d´une théorie sur las structures des crystaux", introducing the idea of seven basic unit cells. From a single "forme primitive" (the first unit cell) by adding other unit cells a crystal could grow (this concept predates also the modern theory of crystal nucleation).

Fig.1. Haüy´s seven unit cells, note the numbering, from "Eassai d´une théorie sur las structures des crystaux" (1784).

 

Fig.2. & 3. Wooden crystal model based on Haüy´s work, made in 1805 in Paris. As certain symmetries are repeated in crystals of a mineral, Haüy concluded that a mineral is made up by smaller, basic chemical units - he called them "molecule intergrante" - symbolized here by the small cubes, forming both a larger cube as a rhombus (both characteristic shapes of the cubic crystal system). More than 500-1000 wooden models were made after 1801, some sets commissioned by Haüy himself. Most models show simple crystals with smooth faces, only 20 complex models, showing the structure with the unit cells, survive.

 

Haüy´s work was quite influential for later mineral classification. In his popular book "Über die oryktognostische Classification nebst Versuchen eines auf blossen äußeren Kennzeichen gegründeten Mineraliensystems" (The genetic-geological classification and an attempt to introduce a mineral-system based on superficial properties, published 1804) the German mineralogist Carl Friedrich Christian Mohs (1773-1839) combines various physical properties of minerals (like color, hardness and density) with crystal models to identify 183 different minerals. 
From there the use of simplified crystal geometry to identify minerals was quickly adopted by other naturalists and the classification of crystals based on the seven unit cells / crystal systems of Haüy is still in use today.

Fig.4. Carl Linnaeus "Systema Naturae", published in 1770, in his work Linnaeus didn´t not only classify animals and plants, but also minerals. One element used to identify minerals were the various crystal shapes, here still displaying a confusing variability.

Geology and Generals: How Geology influenced the Gettysburg Campaign (Part I.)

“Hence the saying: If you know the enemy and know yourself, your victory will not stand in doubt; if you know Heaven and know Earth, you may make your victory complete.” The Art of War, by Sun Tzù

In 1863, after more than two years of Civil War, the Confederate Army of Northern Virginia launches a decisive attack towards the north, in direction of the town of Harrisburg in Pennsylvania. Spotted by the Union Army a skirmish near the small farm town of Gettysburg starts, soon escalating into one of the bloodiest battles in U.S. history. In three days (July 1 to July 3) nearly 50.000 Americans were killed or wounded.  The outcome of this military campaign and battle was strongly influenced by geological events almost one billion years in the making.

The Age of Cryptozoon – In Search of the “Hidden Life”

In the first edition of “On the Origin of Species” (1859) Darwin only briefly addresses the earliest known fossils, or better the lack thereof:

“If the theory [of evolution] be true, it is indisputable that before the lowest Cambrian stratum was deposited, long periods elapsed . . . and the world swarmed with living creatures. [Yet] to the question why we do not find rich fossiliferous deposits belonging to these earliest periods . . . I can give no satisfactory answer.“

The supposed lack of fossils older than 500 to 1.000 million years was not only the result of the “imperfection of the geological column“, as Darwin argued, nor the yet incomplete geological survey of most areas. At the time nobody could really imagine how the earliest organisms on earth – and especially their petrified remains – would look like, so what to search for ?

Vitruvian Geology – Leonardo da Vinci and the Realistic Depiction of the Earth’s Surface

Leonardo da Vinci studied rocks and landscapes not only to improve the realism of his paintings, but also in an attempt to understand how the earth works. Leonardo was obsessed with water, which he considered a vector to erode ancient rocks and to deposit new sedimentary rocks, reshaping so over time the “living” earth. The running water is for earth what blood is for the human body – it flows from the mountains to the sea, then – so Leonardo – in subterranean veins returns to the mountains, a circulatory system like found in humans.

The Harmony of Colors

The first "geological" maps used symbols to characterize single outcrops; later maps introduced shaded areas to display the distribution of specific rock-types, but due the high printing-costs these maps were printed only in black & white, making them hard to read - so let´s put some colors on that map...

A Concise History of Geological Maps: From Outcrop to the first Map

March 23, 1769 marks the birthday of pioneering stratigrapher William Smith, who is also credited with creating the first useful geological map, however like many other great accomplishments also Smith’s idea of depicting the distribution of rocks on a topographic map didn’t materialize out of nowhere.

Pompeii – a Geological Movie-Review : Introducing the Main Character

The new movie “Pompeii” reconstructs one of the most famous volcanic eruptions in history with unprecedented “3D” special effects – but even the best visuals can’t help if the science is wrong – so how geological accurate is the movie ?

Mount Vesuvius as reconstructed in the new film “Pompeii” (from the movie trailer – copyright for it is most likely owned by either the publisher or studio, it is believed that the use of low-resolution images for discussion and education purpose qualifies as fair use under United States copyright law).

The Man who made Mountains

U.S.G.S. engineer Bailey Willis († February 19, 1949) was known for his unorthodox approach to geological questions. Puzzled by the geological structures he discovered in mountain ranges, long before computer-models were available, he constructed a machine to simulate the mountain-forming process.