Sio4 4– tetrahedra join with ions to produce the mineral olivine in the rock peridotite.

Answer;

Independent; Mg2+ and Fe2+

-Independent SiO4 4– tetrahedra join with Mg2+ and Fe2+ ions to produce the mineral olivine in the rock peridotite.

Explanation;

-The silicon-oxygen tetrahedron is a four-sided figure with a silicon atom in the middle bonded to four neighboring oxygen atoms.The simplest silicate structure, that of the mineral olivine, is composed of isolated tetrahedra bonded to iron and/or magnesium ions.

-Olivine is the name of a group of rock-forming minerals that are typically found in mafic and ultramafic igneous rocks such as basalt.  Olivine is a magnesium iron silicate with the formula (Mg2+, Fe2+)2SiO4. Silica tetrahedra, made up of silicon and oxygen, form chains, sheets, and frameworks, and bond with other cations to form silicate minerals.

the truman doctrine was an american foreign policy whose stated purpose was to counter soviet geopolitical expansion during the cold war. it was announced to congress by president harry s. truman on march 12, 1947, and further developed on july 12, 1948, when he pledged to contain threats to greece and turkey.

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.