Five of the six meteorite stones on display at Government Museum in Egmore here have been reported missing.

Museum officials suspect the stones, which are 50 to 75 years old, may have been stolen on Saturday or Sunday, when the galleries remain open and the offices are closed. Only three gallery security guards and an officer are on duty during weekends.

The stones were showcased in one of the galleries of the geology section. Following a complaint from the museum authorities, the Egmore police on Tuesday registered a case. “The theft came to our notice on Monday morning, and we have constituted an investigation panel in the department to look into the incident,” Commissioner of Museums T.S. Sridhar said.

The knob of the wooden and glass case, in which the stones were kept, was opened using a nail, suspect museum officials. The glass is intact. The museum attracts more than 1,000 visitors on weekends, they said.

Of the missing items, three were stony meteorites and two, iron meteorite stones. They weigh between 62 gm and 527 gm and were procured from Madurai, Malabar and Kochi at different times, said Thulasi Brinda, curator of the geology gallery. The gallery is the oldest among the 48 in the museum, dating back to 1851. “This is the first major theft in the museum,” Mr. Sridhar said.

Though all galleries of the museum are under CCTV surveillance, the cables in the geology gallery had been disconnected to facilitate renovation work in the building, said Ms. Brinda.

Mr. Sridhar, however, said that the reasons for stealing the stones were not known, since their commercial value was not significant. “These stones are mainly used for scientific research purposes to know the composition of matter and properties of different elements.”

Meteorite stones are quite common, and it is difficult for people to differentiate them from regular stones, said Mr. Sridhar.

Museum officials said the stones might have been mistaken for antique objects.

Forensic experts visited the museum on Monday for preliminary investigation. The special team formed to narrow in on the culprit questioned other staff members, besides questioning the three security guards and the officer on duty, said Mr. Sridhar.