Hatrurim Formation, Negev desert, Israel

The Hatrurim Formation is largely composed of an unusual rock type, a type of natural portland cement formed by high-temperature alteration of late Cretaceous to lower Eocene bituminous chalk, marl and impure limestone. Several of the type locality mineral species here had previously been intensively studied as anthropogenic phases in portland cement. Unlike calc-silicate rocks in other parts of the world, which were normally created by contact metamorphism (heating by an igneous intrusion), the Hatrurim Formation is underlain by unaltered sedimentary rocks with no igneous intrusion. The origin of the heat which metamorphosed these rocks was long a mystery, but is now thought to be due to oxidation of bituminous compounds (in simple english, it burned). Intensity of metamorphism correlates to access to oxygen. Hydrocarbons are widespread in surrounding rocks but are absent in the metamorphosed beds (the "Mottled Zone", an old name for the Hatrurim Formation).

The Hatrurim Formation was named for the locality Hatrurim, its largest area of exposure, but it also outcrops in several other parts of Israel and Palestine and Jordan too, so not all of the listed minerals may really be from Hatrurim, and many samples loosely labeled "Hatrurim" ought really to have been labelled "Hatrurim Formation" from other localities. See under: Har Ye'elim, Hatrurim, Kefar Uriyya, Malhata, and Nahal Ayalon in Israel; and Beit Sahur, Jebel Harmun, Ma'ale Adumim, Nabi Musa, and Tarqumiya in Palestine; and Daba Siwaqa, Seweilih and Maqarin in Jordan.

References:
- Gross, S. (1977): The Mineralogy of the Hatrurim Formation, Israel. Geological Survey of Israel, Bulletin no. 70, 80 pp.

- Vapnik, Y., Sokol, E., Murashko, M., Sharygin, V. (2006): The enigma of Hatrurim. Mineralogical Almanac, 10, 69-77.