Resistive, magnetoresistive and magnetic properties of four kinds of pressed powders of CrO₂, synthesized from chromic anhydride by the hydrothermal method were investigated. The new synthesis method allows the thickness of dielectric shells to be controlled. The powders consisted of particles (≈ 120 nm in dia.) or acicular crystals (≈ 22.9 nm in dia. and 302 nm in length). All the particles were covered with a surface dielectric shell of different thickness and types (e.g. β-CrOOH oxyhydroxide or chromium oxide Cr₂O₃). The influence of properties and thickness of intergranular dielectric layers as well as shapes of CrO ₂ particles on tunnel resistance and magnetoresistance (MR) of the pressed powders was studied. It was found that at low temperatures all the samples studied displayed a nonmetallic temperature dependence of resistance and a giant negative MR. Maximum values of MR at T ≈ 5 K were ≈ 37% in rather low fields (0.5 T). As temperature was increased, MR decreased rapidly (down to ≈ 1% in field 1 T at T ≈ 200 K). At low temperatures the powders with acicular particles exhibited a new type of MR hysteresis and nonmonotonic dependence of MR with increasing magnetic field (a maximum). A nonmonotonic temperature dependence H_p(T), where H_p being a field in which the resistance is maximal, discrepancies in the values of H_p and coercive force H_c, and anisotropy of MR as a function of mutual orientation of transport current and magnetic field were observed.