Crystal Clear

While minerology may be amongst the most boring sciences (even geology has the flare and burn of sub-crustal movement to garner interest, and the phrase ‘supervolcano’ to boot), the language minerology uses to describe fractal shapes and properties are beautiful, even poetic. It’s appropriate, given how much considered precious by humanity falls under its study: gold, rubies, emeralds, sapphires, silver, diamonds, just to name a few.

Pyroxene twinned crystal line drawing.

(Pyroxene twinned crystal line drawing)

Lest any minerologists get up in arms by my initial claim, I’d like to point out the Natural History Museum’s Hall of Minerals as example. A dead end trapping weary families of tourists after they’ve slogged through the ‘controversial’ Hall of Human Origins and taxed themselves feigning interest in the Hall of Meteorites (the only thing more boring than minerology; sorry space rocks, you may unlock the secrets of the universe but when put on display you’re just a big rock sitting there), the Hall of Minerals remains trapped in the 70s, offering an industrial shag variant with all surfaces carpeted, as the site claims, ‘to simulate the interior of a cave’.

Tetrahedrite twinned crystal structure line drawings.

(Tetrahedrite twinned crystal structure)

People like oggling the displays of large gemstones, guessing how much they’d cost, but few can muster interest in the enormous chunk of azurite/malachite ore once known as ‘The Singing Stone’ (fluctuations in humidity before climate control caused parts to resonate), or do more than glance at the display of sulfur minerals . This is the creme de la creme of American mineral and gem collections and the museum tries its darndest to capture the imagination, but the ratio of people enraptured by facts about ore extraction vs people slumped on carpeted seats with their children running pell mell is about 1:50.

Pyrite twinned crystal structure

(Pyrite twinned crystal structure)

That said, just listen to the language employed describing what really should be a more fascinating area of study (from Wikipedia; bold text are my highlights):

Luster indicates the way a mineral’s surface interacts with light.
Metallic/Splendent -high reflectivity like metal: galena and pyrite
+ Adamantine – brilliant, the luster of diamond also cerussite and anglesite
+ Vitreous -the luster of a broken glass: quartz
+ Pearly – iridescent and pearl-like: talc and apophyllite
+ Resinous – the luster of resin: sphalerite and sulfur
+ Silky – a soft light shown by fibrous materials: gypsum and chrysotile
+ Earthy – shown by finely crystallized minerals: the kidney ore variety of hematite
Greasy lustre

Proustite crystal

(Proustite crystal)

Optical phenomena include Asterism, the display of a star-shaped luminous area.

Aventurescence (or aventurization) is a reflectance effect like that of glitter.

Chatoyant minerals display luminous bands, which appear to move as the specimen is rotated.

Schiller, from German for “twinkle”, is a term used to describe the metallic iridescence originating from below the surface of a stone occuring when light is reflected between layers of minerals.

Fracture- Hackley is jagged fracture with sharp edges.

Fluorite and Quartz crystal

(Fluorite and quartz crystal)

Polymorphism refers to the ability of a solid to exist in more than one crystalline form or structure. According to Gibbs’ rules of phase equilibria, these unique crystalline phases will be dependent on such intensive variables as pressure, temperature and volume.

Nucleation can be either homogeneous, without the influence of foreign particles, or heterogeneous, with the influence of foreign particles.

A crystal or crystalline solid is a solid material, whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions.

A noncrystalline material, which has no long-range order, is called an amorphous, vitreous, or glassy material. It is also often referred to as an amorphous solid, although there are distinct differences between crystalline solids and amorphous solids: most notably, the process of forming a glass does not release the latent heat of fusion.

Realgar on Calcite

(Realgar on calcite)

Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. A twin boundary or composition surface separates the two crystals. Crystallographers classify twinned crystals by a number of twin laws. These twin laws are specific to the crystal system.

Twin boundaries are partly responsible for shock hardening and for many of the changes that occur in cold work of metals with limited slip systems or at very low temperatures. The motion of twin boundaries is responsible for the pseudoelastic and shape-memory behavior of nitinol, and their presence is partly responsible for the hardness due to quenching of steel.

Soft matter or Soft condensed matter is a subfield of condensed matter comprising a variety of physical states that are easily deformed by thermal stresses or thermal fluctuations.

Pierre-Gilles de Gennes has been called the “founding father of soft matter.

The word “crystallography” is derived from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and graphein = write.

Neutrons are scattered by the atomic nuclei through the strong nuclear forces, but in addition, the magnetic moment of neutrons is non-zero.

Tri-Color Tourmaline

(Tri-color tourmaline)

*Crystal structure drawings by R.Weller/Cochise College

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