1. THE METHOD OF IMPARTING FLEXIBILITY AND CRACK- AND IMPACT-RESISTANT STRENGTH PROPERTIES TO A MAGNESIUM OXYCHLORIDE ARTICLE WHICH COMPRISES: (1) ADMIXING, WITH MGO AND MGCL2 IN AQUEOUS SOLUTION IN THE PROPORTIONS OF BETWEEN ABOUT 2 AND ABOUT 7.5 PARTS OF MGO PER 100 PARTS OF MGCL2 BY WEIGHT, BETWEEN ABOUT 1% ABOUT 20% OF DEXTRIN, BASED ON THE WEIGHT OF MGO PRESENT; (2) REACTING THE MIXTURE SO MADE AT A TEMPERATURE AT LEAST AS HIGH AS ROOM TEMPERATURE, ACCOMPANIED BY STIRRING, UNTIL A SLURRY OF ELONGATED MAGNESIUM OXYCHLORIDE FIBRILS CONTAINING THE DEXTRIN FORMS, AND THEREAFTER DISCONTINUING STIRRING TO PERMIT A PRECIPITATE OF THE FIBRILS TO SETTLE; (3) SEPARATING THE ELONGATED FIBRILS OF MAGNESIUM OXYCHLORIDE CONTAINING THE DEXTRIN, SO MADE; (4) ADMIXING WITH THE FIBRILS BETWEEN ABOUT 5% AND ABOUT 75%, BY WEIGHT THEREOF, OF A RESIN SELECTED FROM THE CLASS CONSISTING OF MONOMERIC STYRENE TOGETHER WITH A POLYMERIZATION CATALYST THEREFOR, POLYSTYRENE DISSOLVED IN AN ORGANIC SOLVENT, AND A LIQUID EPOXY RESIN HAVING A HARDENING AGENT ADMIXED THEREWITH WHICH CONVERTS AN EPOXY RESIN TO AN INFUSIBLE SOLID UPON STANDING; (5) SUBJECTING THE RESULTING COMPOSITION TO A TEMPERATURE OF BETWEEN ABOUT ROOM TEMPERATURE AND ABOUT 200*C. FOR A TIME SUFFICIENT TO CONVERT THE RESIN PRESENT TO AN INFUSIBLE SOLID THEREBY PROVIDING A HIGH STRENGTH CRACK-RESISTANT ARTICLE COMPOSED OF INTERLOCKING MATRICES, ONE OF THE MAGNESIUM OXYCHLORIDE FIBRILS AND THE OTHER OF THE CROSS-LINKED RESIN.