Specific heat at 25° C

The heat capacity of a substance measures the ability of a substance to retain heat. The heat capacity is that quantity of heat required to raise a substance one degree in temperature. The specific heat is the heat capacity per gram of substance. The more loosely the components of a solid is held, the higher is the substance's specific heat.

Form of Carbon	Specific Heat (calories / gram*° K)
Graphite	0.170
Diamond	0.124

 

Thermal conductivity at 25° C

Form of Carbon	Thermal Conductivity (Watts/centimeter * ° K)
Graphite	19.6 parallel to sheets 0.0573 perpendicular to sheets
Diamond	23.2
Amorphous	0.0159
C60

Thermal energy within a crystalline solid are conducted by electrons and/or discrete vibrational energy packets (phonons). A material's ability to conduct heat is known as its thermal conductivity.

The reason why one substance feels "cooler" than others at the same temperature is because of the difference of their thermal conductivity. The thermal conductivity of a substance gives a rough indication for how rigidly components within a crystalline solid are held together and how much imperfections are incorporated within a crystal. Moving components within a substance tend to scatter the heat carrying electrons and phonons, in effect reduce the thermal conductivity of that material. A prime example is that shown by graphite.

Different directions in a crystal can conduct heat at different rates. Graphite exhibits this behavior. It is highly conducting along its layers and not so well perpendicular to the layers because their is no bonding between the layers.

Do you know that you can distinguish between a real diamond and cubic zirconia by their thermal conductivity. The diamond has a higher thermal conductivity than the latter, so feels cooler to your lip.