The structural parameters of optically controlled cubic Mn I boracite, Mn3B7O13I, and Mn Br boracite, Mn3B7O13Br, were refined on single crystals at 421 and 580 K, resp. (space group F.hivin.43c, Z = 8). To perform these measurements, a low-cost heating device, based on a soldering Fe heating element, was used. Cell parameters are 12.3404(3) .ANG. for Mn I boracite and 12.3100(9) .ANG. for Mn I boracite and 12.3100(9) .ANG. for Mn Br boracite. The cell parameters and the deviation from planarity of the O environment around the metal ion are greater in Mn boracites than in other known cubic boracites. At. coordinates are given.