Zirconium carbide and zirconium nitride are refractory solids. Zirconium hydride describes an alloy made by combining zirconium and hydrogen. Ceramic fillers include zirconia-silica and zirconium oxide. All unstable isotopes of molybdenum decay into isotopes of zirconium, niobium, technetium, and ruthenium. Mesoporous oxides of niobium, tantalum, titanium, zirconium, cerium and tin have also been reported. Rubidium, strontium, yttrium, zirconium, and niobium have no biological role. Some contain denitriding metals such as titanium and zirconium to avoid nitrogen porosity. It is isomorphous to transition metal tetrachlorides of zirconium, hafnium, and platinum. Mineral sands are the predominant type of titanium, zirconium, and thorium deposit. In many ways, niobium is similar to tantalum and zirconium. Intensities of zirconium and titanium may be indicated explicitly. Zirconium hydride phases are also known. This process for differential purification of zirconium and hafnium is still in use today. When heated with carbon, it converts to zirconium carbide.