Spherical and rod-shaped proppants and anti-flowback agents made from sillimanite minerals possess high strength and high conductivity. The sillimanite minerals may be selected from the group consisting of kyanite, sillimanite, and andalusite and may be used alone or in combination with other materials, such as bauxite, kaolin, meta-kaolin, pure or technical grade alumina (about 98%-99.9% alumina by weight), alumina-containing slag, zirconia, silica, iron, alkali elements (such as calcium, magnesium, and sodium), and virtually any other mineral containing alumina. The starting material may optionally be milled to achieve better compacity and crush resistance in the final proppant or anti-flowback agent. A fracturing fluid may comprise the rods or spheres alone, or in combination with each other or other proppants or anti-flowback agents of different shapes.