Magnetic particles are prepared containing a magnetic core coated with a
glass layer having a substantially pore-free class surface or having pores
with a diameter offices than 10 nm. The particles are used for separating
biological material such as nucleic acids. A preferred process of
preparing the particles is by forming a mixture of magnetic cores with a
sol formed from an alcohol and a metal alkoxide, spray-drying the mixture
to coat the cores with a layer of gelled sol, and heating the coated cores
to obtain the magnetic glass particles. Preferably, the particles have an
average particle size of less than 100 .mu.m. The magnetic core may be a
composite material containing a mica core and magnetite particles
immobilized on the mica core, and the glass layer may contain boron oxide.
Magnetic core materials include magnetite (Fe.sub.3 O.sub.4) and Fe.sub.2
O.sub.3.
