Alexandrite, a rare form of the mineral chrysoberyl named for Tsar Alexander Ⅱ

Discovered in the 1830s in the Ural Mountains in Russia, the mineral alexandrite was named to honor Czar Alexander Ⅱ [1-3]. Alexandrite is a rare form of  chrysoberyl, a transparent, pale yellow-green mineral. By composition, chrysoberyl is beryllium aluminate with the formula BeAl₂O₄. Alexandrite contains impurities of chromium ions (Cr³⁺), which replace less than 0.5% of the aluminum ions (Al³⁺) [3]. This variation in ion-species composition results in a change of light-absorption behavior, making alexandrite appear yellow-green to greenish-blue in daylight and purple-red under artificial light.

In a recent American Scientist infographic, Andy Brunning introduced alexandrite as follows [2]:

Alexandrite is a rare form of the mineral chrysoberyl, which has the chemical formula Al₂BeO₄. Not content with being one color, it can display a whole range of hues, depending on the light falling on it. Deposits of alexandrite were first discovered in the 1830s, in the Ural Mountains in Russia. Mineralogist Count Lev Alekseevich Perovskii presented it to the future Tsar Alexander Ⅱ on his 16th birthday and named it in his honor.

It is interesting to find alexandrite typically associated with the formula BeAl₂O₄—not reflecting its nature of being a chromium variety of chrysoberyl (see, for example, its mindat entry [4]). To annotate data entries and abstracted text as specifically bound to alexandrite, the CurlySMILES language [5] provides the needed syntax: {*BeAl2O4}{IMc=[Cr+3]}. In this notation, the Stoichiometric Formula Notation (SFN) is augmented by annotation code beginning with the miscellaneous interest annotation marker IM for impurity and continuing with the specification of the impurity ion. CurlySMILES further allows integration of text and code. The above notation can be enhanced by explicitly stating the mineral name (using annotation dictionary key min):  
{*BeAl2O4}{IMc=[Cr+3];min=alexandrite} 


Keywords: mineralogy, chemistry, cheminformatics, nomenclature, mineral notation, mineral formula encoding, compact annotation.

References and more to explore

[1] Carly Wickell: Get the Facts About Alexandrite. The spruceCrafts, December 13, 2018. Link: www.thesprucecrafts.com/alexandrite-facts-2042901.
[2] Andy Brunning: The color of alexandrite. American Scientist Jan.-Feb. 2019. 107 (1).
[3] The Mineral Chrysoberyl. Minerals.net. Link: www.minerals.net/mineral/chrysoberyl.aspx.
[4] Alexandrite. Mindat.org. Link: www.mindat.org/min-109.html.
[5] Axel Drefahl: CurlySMILES: a chemical language to customize and annotate encodings of molecular and nanodevice structures. Journal of Cheminformatics 2011, 3:1. DOI: 10.1186/1758-2946-3-1.

Felsina → Bononia → Bologna

The city of Felsina was founded by Etruscans over 2,500 years ago on the edge of the Po Plain. This is the site of modern Bologna in the Emilia-Romagna Region of Northern Italy. During early Roman times, the city was called by its Latin name: Bononia, derived from the Celtic word for settlement. In fact, the city was refounded and resettled several times. For example, Bononia was founded in 189 B.C. as a Latin colony, where Felsina had stood before it had fallen to invading Gauls [1-4].

The history of “modern Bologna” starts in 1088, when the city became the seat of the oldest university (of in what is defined as the western world). Bologna grew as an expanding university and today is an open-air museum. You may not be a mathematician, but you may nevertheless enjoy the introduction to Bologna in the Summer 2018 “Mathematical Tourist” column of  “The Mathematical Intelligencer,” which begins as follows [4]: 

Bologna was founded by the Etruscans, who called it Felsina. It was named Bononia by the ancient Romans, perhaps because of the presence in its territory of the Boii Celts. Although it is a city full of history and art, it is less frequented by tourists than other Italian cities like Venice, Florence, or the eternal Rome. Few of those tourists know, however, that it was one of the first cities in the world to have legislation for the protection of cultural assets [...].This makes Bologna a kind of open-air museum; walking through its streets, one may come across works of art or archaeological finds that in other cities are found only within museums.
                                             Gonzáles, Rabiti, and Cartwright, 2018

Bologna—a city of multiple firsts, many outdoor attractions and of scientific and mathematical significance.

Keywords: geography, place names, history, Boii Celts, Northern Italy.

References and more to explore

[1] Felsina. ENCYCLOPÆDIA BRITANNICA. Internet: www.britannica.com/place/Felsina.
[2] Bononia. Wiktionary. Internet: en.wiktionary.org/wiki/Bononia.
[3] Felsina/Bononia. PLEIDES. pleiades.stoa.org/places/393421.
[4] Stillwell, R. and MacDonald, W. L. The Princeton Encyclopedia of Classical Sites. Princeton University Press, Princeton, New Jersey, 1976; page 158.
[5] Gonzáles, D.L., Rabiti, L. and Cartwright, J. H. E. Bonaventura Cavalieri and Bologna. The Mathematical Intelligencer, Summer 2018, 40 (20), 21-29. DOI: 10.1007/s00283-018-9779-5.