@article {Walvoort2001MG,
	title = {{Compositional Kriging: A Spatial Interpolation Method for Compositional Data}},
	journal = {Mathematical Geology},
	volume = {33},
	number = {8},
	year = {2001},
	pages = {951-966},
	author = {Walvoort, D.~J.~J. and {de Gruijter}, J.~J.}
}