Ceramic spheroids having low density and high crush resistance

Fired ceramic spheroids having:

• A. a core:
• 1. made from raw materials comprising about:
• a. 50 to 99.8 parts by weight mineral particulates,
• 0.1 to 50 parts by weight silicon carbide, and
• 0.1 to 15 parts by weight binder;
• 2. wherein the mineral particulates comprise a mineral mixture which has a fired density of less than about 2.9 grams per cubic centimeter when fired above about 1100.degree. C. and includes at least one mineral having chemically bound water or sulphur, in a form which is not substantially water soluble, in amounts sufficient to yield 0.5 to 5.0 weight percent water or 0.04 to 2.0 weight percent sulfur in the total mass of mineral particulates;
• 3. wherein the binder is characterized by adhering the raw materials together after they are converted to spheroids but before they are fired;
• 4. said core having a plurality of closed air cells;
• and
• B. an outer shell, surrounding the core, comprising a metal oxide selected from aluminum oxide and magnesium oxide;
• said fired ceramic spheroids having a fired density less than about 2.2 grams per cubic centimeter.