Provided is a method for producing a seamless tube, in which after a starting material to be extruded has been heated to a heating temperature T [°C] satisfying the relationship of Formula (1) or Formula (2) depending on the outside diameter do [mm] thereof, the starting material is hot-extruded by providing a solid lubricating glass between the starting material to be extruded and a die, whereby a transverse flaw on the outer surface in the top portion of tube can be prevented when hot-extrusion is performed by using a starting material for extrusion having low deformability at high temperatures. When d₀<200, T ≤ 1250+1.1487xA-7.838×ln(t₀/t)-10.135×ln(d₀/d) ... (1); when d₀≥200, T ≤ 1219+1.1487xA-7.838×ln(t₀/t)-10.135×ln(d₀/d) ... (2), where A = L/V_av × 1000 [msec], V_av = (V₀ + V₀×ρ)/2 [mm/sec], p = (t₀×(d₀-t₀))/(t×(d-t)), t₀: wall thickness of starting material to be extruded [mm], d: outside diameter of extruded tube [mm], t: wall thickness thereof [mm], L: length of approach portion of die along extrusion direction [mm], and V₀: ram speed [mm/sec].

Asbestiform crystalline calcium M phosphate, where M is sodium or lithium, typically having a length to average diameter ratio of at least 5:1, can be prepared by forming a melt of a source of oxygen, calcium, phosphorus and M having a mole ratio of about 15 percent to about 30 percent M₂0, about 48 percent to about 60 percent P₂O₅ and about 20 percent to about 37 percent CaO, cooling the melt within the range of about 500°C. to about 750°C. for a sufficient time to permit blocks of calcium M phosphate to form, and fiberizing the blocks into the asbestiform crystals. Such asbestiform crystalline calcium M phosphates are useful to prepare composites of organic polymeric materials.