Ternesite

Information about Ternesite

Ternesite is a rare calcium silicate sulphate mineral found in two quite different settings – the thermally metamorphosed volcanic xenoliths of the Eifel district in Germany, and the burnt and altered limestones of industrial slag heaps – and which has attracted growing interest from cement chemists for its potential as a component of low-carbon cement clinker. It is primarily a scientific specimen rather than a showy collector’s mineral, but fine examples from the Eifel show an unexpected and striking blue colour.

At the Ettringer Bellerberg, its type locality, ternesite was originally described as a bright blue mineral in calcium-rich xenoliths – fragments of limestone rock caught up in basalt lava and subjected to intense heat. This colouration, attributed to trace iron and titanium impurities, makes Eifel material immediately distinctive; most specimens from slag localities are white to colourless or very pale yellow. Crystals form radially arranged prismatic groups, typically only a few millimetres across, with a vitreous lustre.

Ternesite forms at high temperatures – above around 900-1000°C – through the reaction of calcium silicate minerals with anhydrite or other sulphate-bearing phases. In volcanic settings this happens when limestone xenoliths are engulfed and partially melted in basalt lava flows. In industrial settings it forms in lime kiln wall coatings, furnace sinters, and in the high-temperature zones of burning colliery spoil heaps. The synthetic compound was known to chemists from as early as 1966, and the crystal structure was solved from synthetic material in 1974, well before the natural mineral was formally described in 1997. Above approximately 1230°C ternesite breaks down to a high-temperature polymorph of dicalcium silicate with loss of sulphur dioxide gas.

Uses and History

Ternesite has no gemological applications. As a natural mineral it is collected purely as a scientific specimen. However, its industrial significance is growing: ternesite-based cement clinkers have been identified as a potential route to lower-carbon cement production, because ternesite can be synthesised at lower kiln temperatures than conventional Portland cement clinker phases, reducing energy input and associated CO2 emissions.

The best collector specimens come from the Ettringer Bellerberg itself and the Caspar quarry at Ettringen – the same productive volcanic district responsible for zeophyllite, willhendersonite, and other rare Eifel species found elsewhere on this site. The Lapanouse-de-Sevérac slag locality in Aveyron, southern France, is the other well-documented source of collectable material. No occurrences are currently recorded from the United Kingdom.

Mineralogy

Hazards and Warnings

No specific health risks have been formally recorded for ternesite. Mineral collectors should wash their hands after handling specimens as a matter of good practice.

Almost all rocks, minerals (and, frankly, almost all other substances on earth) can produce toxic dust when cutting, which can cause serious respiratory conditions including silicosis. When cutting or polishing rocks, minerals, shells, etc, all work should be done wet to minimise the dust, and a suitable respirator or extraction system should be used.

Translations

Further Reading / External Links

• https://en.wikipedia.org/wiki/Ternesite
• https://www.mindat.org/min-7330.html
• https://link.springer.com/article/10.1007/BF01163138
• https://www.handbookofmineralogy.org/pdfs/ternesite.pdf