The aluminosilicates form a large group of minerals based on linked AlO₄ and SiO₄ tetrahedra which includes many clay and zeolite minerals whose compositions may be written M^x+[Al_xSi_1−xO₄]^x−. Discuss the occurrence of the BeO₄ unit in natural minerals. To what extent has it proved possible to produce beryllophosphates based on linked BeO₄ and PO₄ tetrahedral units that are structural and compositional analogues of M^x+[Al_xSi_1−xO₄]^x−, that is M^x+[Be_xP_1−xO₄]^x−?