Matt examined a map showing the mineral resources of the United States. He saw there was a great concentration of different minerals in the western area of the country. Explain three ways that minerals form and why they are so concentrated on the west coast. Map of North America with key. Key lists the following: pale gray triangle = Copper; diamond shape = Diamond; slightly darker gray triangle = Gold; slightly darker triangle = Iron; black triangle = Lead-Zinc; light gray triangle = Silver. The west side of the continent has between 50 to 100 triangles of all colors along the coast. There are 4 black triangles and two darker triangles in the mid-east portion of the US. There are about 30 triangles in the North East part of the US and the South East part of Canada. There are two diamonds and fewer than 10 triangles in the Northern part of Canada.