Lorentz transformation, but mass cannot be transformed into another form:

It's nice to say that where there's mass, there's energy, but not always it's actually the opposite.

Because some forms of energy exist without being converted into mass. such as massless energetic subatomic particles, such as photons.

A photon absorbed by an electron is not converted into mass but remains there as electron energy, without changing the electron's mass.

Mass is converted into energy by nuclear reactions of atoms, especially through fission and fusion, or spontaneous radioactive decay in unstable atoms.

Otherwise, mass is not converted to pure energy without nuclear reactions but instead energy is stored in the mass without consideration of the wave speed.

In mass-energy conversion, 1 kg m^2/sec^2 mass of energy is called 1 Joule. Thus, the Joule is a derived unit of energy in SI units.

The electron volt (eV) is a unit of energy.

1 eV = 1.6 * 10^-19 J.

In particular, small amounts of mass are turned into energy from the breaking up through fission, or by combination through fusion of the nuclei of atoms. 

Even spontaneous radioactive decay converts some mass into incredible amounts of energy.

In conclusion, Lorentz's transformation of mass into another form is physically false.