硅卡岩是中性的侵入岩和碳酸盐类岩石，在接触带经气化高温热液交代作用形成的一种变质岩，如果原岩为石灰岩，形成的富钙硅酸盐矿物为钙质硅卡岩；如果原岩为白云岩，形成的富镁硅酸盐矿物为镁质硅卡岩；围岩中的硅卡岩统称外硅卡岩；有时岩体边缘蚀变形成的硅卡岩，称为内硅卡岩。它主要是石榴石和透辉石，其次为角闪石、绿帘石、石英所组成。

硅卡岩比重大（3.3-3.9)，颜色有褐色、红色、绿色、黑色、灰色等各种，结构有块状、斑杂状、条带状等，有等粒或不等粒。

硅卡岩伴生有许多种矿物，如铁、铜、铅、锌、钼、钨、锡、硼、金云母等。

Skarns or tactites are calcium-bearing calc–silicate rocks. Skarns are most often formed at the contact zone between intrusions of granitic magma bodies and carbonate sedimentary rocks such as limestone and dolostone. Hot waters derived from the granitic magma are rich in silica, iron, aluminium, and magnesium. These fluids mix in the contact zone, dissolve calcium-rich carbonate rocks, and convert the host carbonate rock to skarn deposits in a metamorphic process called metasomatism. The resulting metamorphic rock may consist of a very wide variety of minerals dependent largely on the original composition of the magmatic fluids and the purity of the carbonate sedimentary rocks.