Vein and hydrothermal . sedimeOI~ry types of magnesite
from eastern Iran probably originated from ascending
hydrothermal solutions. The cryptocryistalline magnesite is very
pure although it has a variable CaO/Si02 ratio. It is compact with
a very fine and uniform texture. The mineralogy of samples of
dead burned magnesites calcined at different temperatures and
times arc variable and can be predicted from phase equilibria
studies. The textural relationships studied using scanning electron
microscopy show that matrix is concentrated at peric1ase crystal
boundaries particularly at the triple points. The periclase crr-itals
are larger at increased calcination temperatures and times. The
amount of periclase - Periclase grain contact reduces by increasing
the amount of impurities.
Electron microprobe results confirm that CaO and FeO in
periclase increase steadily with the increase in the CaOlSi02 ratio
and FeO content of bulk chemistry respectively.
The mineral chemistry of forsterite. monticellite. merwinite,
dicalcium silicate and tricalcium silicate in dead burned magnesite
indicate some solid solution between some phases, although
sometimes it is difficult to analyse single phases. This study
indicates that high quality dead burned magnesia bricks can be
produced from the Iranian natural magnesite with low CaO , Si02
and FeO impurities and by maintaining the CaOlSi02 ratio of
around 2:1.