Itrongay (Itrongahy), Mahasoa East Commune, Betroka District, Anosy (Fort Dauphin) Region, Tuléar (Toliara) Province, Madagascar

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Itrongay, Kaominina Mahasoa Atsinanana (Est), Distrikan'i Betroka, Faritra Anosy, Faritanin'i Toliary, Madagasikara

The designation Itrongahy refers to an area famous for yellow gemmy "orthoclase" (Fe3+ substituting for Al3+)(which actually are sanidine, see below), but also gemmy crystals of diopside and zircon. In 1922 when the famous french mineralogist wrote his monumental book on malagasy minerals, (Lacroix 1922), the ancient village called Itrongay was situated on the path between the town Betroka and Benenitra in the southern Madagascar. It was located near the village which today is called Tongay, south of the river Hazofotsy. Itrongay was at that time an important mineralogical center in the area. But today you will not find the name "Itrongay" on contemporary maps- just the geological ones.

The famous gemmy orthoclase is today found in a 40 km large area around what was the ancient Itrongay. In lack of local knowledge, minerals from this area and others close by are still labelled as Itrongay by mineral dealers. Some of the minerals found today originates from the area around Benono.

NOTE 1: Not all gemmy feldspar labelled Itrongay, originates from the Itrongay area. In the 1980s gemmy orthoclase were also found at Ampandrandava (Pezzotta 1999). It is also reported from other localities in the the Betroka district as well.
Not all the minerals refered to in the literature as coming from Itrongay has been found in the same geological setting as the sanidine. And some of the minerals found in the beginning of the 20th century were also found direct on the ground.
Lacroix (1922) states that the diopside and sanidine is originating from a pegmatite. Pezzotta (1999) observes in a new site in the same area that the yellow gemmy sanidine occurs in pegmatite derived feldspar veins cutting marbles.

NOTE 2: X-ray studies of a bright yellow to colorless feldspar collected in 2001 at one of the localities around Itrongay and other samples showed it to be high to low sanidine, not orthoclase (Simmons and Falster 2002). Further investigations by Ackermann at al (2005) on the cation distribution and ordering of Si, Al, Fe on the tetragonal (T1) site of a K-feldspar from Itrongay, showed it to be a monoclinic low sanidine (for more details see the paper at http://www.escholarship.org/uc/item/20f968sx

See also the discussion under http://www.mindat.org/mesg-7-162698.html and

http://www.mindat.org/mesg-7-219075.html

Mineral List

Albite 'Apatite' 'Bastnäsite' Beryl Biotite Calcite 'Chevkinite'

Diopside Epidote Ilmenite 'K Feldspar' Kornerupine Opal Orthoclase

'Perthite' Phlogopite Quartz var: Chalcedony var: Smoky Quartz Rutile Sanidine Sapphirine

'Scapolite' Spinel Titanite Zircon

25 entries listed. 15 valid minerals. 1 erroneous literature entry.

References