Cold working of sodium metal converts body centred sodium metal to a mixture of a hexagonal form and body centred sodium at 5 K. The hexagonal from converts back to the body-centred form at 100-100 K.

Cold working of lithium metal converts body centred lithium metal to a mixture of a hexagonal form and body centred lithium at 78 K.

Potassium, rubidium, and caesium retain their body centred structure after cooling

X-ray study of the alkali metals at low temperatures, Barrett, C. S. , Acta Crystallographica, 08/1956, Volume 9, Issue 8, p.671 - 677, (1956)

Crystal structure of uranium nitride, UN. The structure is face-centered cubic with a lattice constant of 4889 ± 0.001 Å at 26°C and sodium chloride type. The theoretical density is 14315 kg m^–3, and the U—N bond distance for coordination number 6 is 2.4449 Å.

Crystallographic Data. 177. Uranium Mononitride, Kempter, Charles, McGuire Joseph, and Nadler M. , Analytical Chemistry, 01/1959, Volume 31, Issue 1, p.156 - 157, (1959)

ScCl₃, TiCl₃ und VCl₃ kristallisieren hexagonal-rhomboedrisch in dem gleichen Gitter wie FeCl₃ (DO₅-Typ).

Die Kristallstrukturen von ScCl3, TiCl3 und VCl3, Klemm, Wilhelm, and Krose Ehrhard , Zeitschrift für anorganische Chemie, 05/1947, Volume 253, Issue 3-4, p.218 - 225, (1947)

BuckyEggAn egg-shaped fullerene, or "buckyball egg" has been made and characterized by chemists in America at UC Davis (California), Virginia Tech, and Emory and Henry College in Virginia. They were trying to encapsulate terbium atoms within fullerenes but instead encapsulated terbium nitride within an egg-shaped fullerene.1

The compound Tb₃N@C₈₄ was synthesized using an arc-discharge generator by vaporizing composite graphite rods containing a mixture of Tb₄O₇, graphite, and iron nitride as catalyst in a low-pressure He/N₂atmosphere. This gave a complex mixture of products and chromatography gave seven terbium-containing fractions, the fourth fraction of which contained two isomers of Tb₃N@C₈₄. Crystallographc studies show the compound from one angle in particular seems very egg shaped! Remarkable! The Tb₃N unit is clearly visible (terbium in green and nitrogen in blue).

Until the publication of this work it was normally accepted that no two pentagons can touch in a fullerene and are always surrounded by hexagons. However in this case there are two pentagons (the 8 atoms at the pointy part of the egg at the top of the attached image) linked as a bent pentalene fragment.

• 1. Tb3N@C84 :  An Improbable, Egg-Shaped Endohedral Fullerene that Violates the Isolated Pentagon Rule,
  Beavers, Christine M., Zuo Tianming, Duchamp James C., Harich Kim, Dorn Harry C., Olmstead Marilyn M., and Balch Alan L.
  , Journal of the American Chemical Society, 09/2006, Volume 128, Issue 35, p.11352 - 11353, (2006)
  

Abstract.The structure of isomer 2 of Tb₃N@C₈₄ has been determined through single-crystal X-ray diffraction on Tb₃N@C₈₄·NiII(OEP)·2(C₆H₆). The carbon cage has a distinct egg shape due to the presence of a single pair of fused pentagons at one apex of the molecule. Thus, although 24 IPR structures are available to the C₈₄ cage, Nature utilizes one of the 51 568 isomeric structures that do not conform to the IPR for this unusual molecule. The Tb3N portion of isomer 2 of Tb₃N@C₈₄ is strictly planar. One Tb atom is nestled within the fold of the fused pentagons, while the other Tb atoms are disordered over four pairs of sites.

Tb3N@C84 :  An Improbable, Egg-Shaped Endohedral Fullerene that Violates the Isolated Pentagon Rule, Beavers, Christine M., Zuo Tianming, Duchamp James C., Harich Kim, Dorn Harry C., Olmstead Marilyn M., and Balch Alan L. , Journal of the American Chemical Society, 09/2006, Volume 128, Issue 35, p.11352 - 11353, (2006)

BuckyEgg Tb₃N@C₈₄: image credit Mark Winter

Ozone. Credit Mark Winter

GypsumThe giant gypsum crystals in Mexico's "Cueva de los Cristales" are a stunning natural wonder featuring crystals up to 11 metres long.

These giant gypsum (hydrated calcium sulphate) crystals in the “Cave of Crystals” in the Naica mine, Chihuahua, Mexico pose an interesting problem: how are they formed. A Spanish-Mexican team led by Prof García-Ruiz et al. propose that these crystals are derived from "a self-feeding mechanism driven by a solution-mediated, anhydrite-gypsum phase transition". The solution from which the crystals grew were maintained in a very narrow, stable temperature range. It seems likely that related features will be discovered in the future.1

See Geology: April, 2007, v. 35, no. 4, where the crystals are featured on the cover.

• 1. Formation of natural gypsum megacrystals in Naica, Mexico,
  García-Ruiz, Juan Manuel, Villasuso Roberto, Ayora Carlos, Canals Angels, and Otálora Fermín
  , Geology, 2007, Volume 35, Issue 4, p.327, (2007)
  

Gypsum, cover from Geology; April 2007; v. 35; no. 4; p. 327-330; DOI: 10.1130/G23393A.11

• 1. Formation of natural gypsum megacrystals in Naica, Mexico,
  García-Ruiz, Juan Manuel, Villasuso Roberto, Ayora Carlos, Canals Angels, and Otálora Fermín
  , Geology, 2007, Volume 35, Issue 4, p.327, (2007)
  

Only carbon from the Group 14 elements forms stable double bonds with oxygen under normal conditions. When frozen, carbon dioxide is known as "dry-ice". A non-molecular single-bonded crystalline form of carbon dioxide (phase V) exists at high pressure according to Italian and French researchers.1

Amorphous forms of silica (a-SiO₂) and germania (a-GeO₂) are known at ambient conditions but only recently has an amorphous, silica-like form of carbon dioxide, a-CO₂. This is labelled a-carbonia and made by compression of CO₂ at room temperature at pressures between 40 and 48 GPa (that's a staggering 400-500 thousand atmospheres).

During this compression, infrared spectra at temperatures up to 680 K show the progressive formation of C–O single bonds and the simultaneous disappearance of all infrared bands associated with molecular CO₂. Raman and synchrotron X-ray diffraction measurements confirm the amorphous character of the CO₂. Vibrational and diffraction data for a-SiO₂ and a-GeO₂ are closely related and calculations also suggest shows that a-CO₂ is structurally homologous to a-silica (a-SiO₂) and a-germania (a-GeO₂).

This research helps to understanding the nature of the interiors of gas-giant planets where carbon dioxide may be squeezed at very high pressures. Maybe it could be used to make very hard glass because it is expected to be very stiff rather like diamond. The researchers ponder whether "small amounts of these new glasses could be of interest for technology applications like hard and resistant coatings for micro-electronics, for example."

• 1. Amorphous silica-like carbon dioxide,
  Santoro, Mario, Gorelli Federico A., Bini Roberto, Ruocco Giancarlo, Scandolo Sandro, and Crichton Wilson A.
  , Nature, 6/2006, Volume 441, Issue 7095, p.857 - 860, (2006)