(Itrongay, Kaominina Mahasoa Atsinanana (Est), Distrikan'i Betroka, Faritra Anosy, Faritanin'i Toliary, Madagasikara)
Area famous for yellow gemmy orthoclase (Fe3+ substituting for Al), but also gemmy crystals of diopside and zircon. Lacroix (1922) states that the diopside and orthoclase is originating from a pegmatite. Pezzotta (1999) observes in a new site in the same area that the yellow gemmy orthoclase occurs in pegmatite derived feldspar veins cutting marbles.
NOTE: Not all gemmy orthoclase labelled Itrongay, originates from 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 litterature as coming from Itrongay has been found in the same geological setting as the orthoclase. And some of the minerals found in the beginning of the 20th century were also found direct on the ground.
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 is called Tongay today, south of the river Hazofotsy. Itrongay was at that time an important mineralogical center in the area. 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.
References:
- Lacroix, A. (1922): Mineralogie de Madagascar, Tome I. Géologie-Minéralogie descriptive. A.Challamel (Éditeur), Paris. 624p.
- Behier, J. (1960): Contribution á la Minéralogie de Madagascar. Annales Géologiques de Madagascar XXIX, Tananarive, 78p
- Behier, J. (1963): Carte mineralogique de Madagascar. Archive Service Géologique Madagascar. A 1871
- Pezzotta, F.(1999): Madagaskar- Das Paradies des Mineralien und Edelsteine. ExtraLapis no.17,30-31[german version]
Mineral List:23 entries listed. 15 valid minerals.
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