Calcification is the process in which calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 salts build up in soft tissue, causing it to harden. Calcifications may be classified on whether there is mineral balance or not, and the location of the calcification.
Calcification of soft tissue (arteries, cartilage, heart valves, etc) can be caused by Vitamin K deficiency

Vitamin K deficiency

Vitamin K deficiency is a form of avitaminosis resulting from insufficient vitamin K.-Causes:Vitamin K-deficiency may occur by disturbed intestinal uptake , by therapeutic or accidental intake of vitamin K-antagonists or, very rarely, by nutritional vitamin K deficiency...

 or by poor calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 absorption due to a high calcium/vitamin D ratio. This can occur with or without a mineral imbalance.

Intake of excessive Vitamin D can cause Vitamin D poisoning

Hypervitaminosis D

Hypervitaminosis D is a state of vitamin D toxicity.The recommended daily allowance is 400 IU per day. Overdose has been observed at 1925 µg/d...

 and excessive intake of calcium from the intestine, when accompanied by a deficiency of vitamin K (perhaps induced by an anticoagulent such as warfarin

Warfarin

Warfarin is an anticoagulant. It is most likely to be the drug popularly referred to as a "blood thinner," yet this is a misnomer, since it does not affect the thickness or viscosity of blood...

).