criteria that might be considered by decision makers and mineral experts is determining a mineral’s criticality and, subsequently, on assessing the type and frequency of information needed at a federal level to mitigate economic impacts should the mineral’s supply become restricted. As a prelude to the criticality assessments, the committee reviews here the materials presented in Chapters 2 and 3 on mineral use and availability. These two chapters inform the “scoring” of the matrix for a specific mineral, or where in the matrix a specific mineral might fall at a given time.

The vertical axis, as noted previously, represents increasing importance in use, or analogously, the increasing impact of a supply restriction for a particular mineral. The methodology uses a relative scale of 1 (low) to 4 (high) to represent different degrees of importance or impact (Figure 4.1).

The key concept in locating a mineral on the vertical axis is substitution—the ease or difficulty of substituting for a mineral that becomes unavailable or too expensive. The position of a mineral on this axis depends on the context, the definition of which considers two important aspects. The first is scale. Are we concerned about a particular product and the impact a supply restriction would have on the performance of a product? Are we concerned about the effects on a local, regional, or national economy should the supply of a mineral essential to a local, regional, or national industry become restricted? Are we concerned about the effect of a supply restriction on a national priority, such as defense? For example, a mineral that is essential to the performance of a product (i.e., no ready substitutes exist to provide the same or similar performance) would be scored as a 4 by the manufacturer of the product. However, if this industrial sector was only a very small part of the national economy, it might be scored a 1 from the perspective of the U.S. economy. The second aspect of the context in placing a mineral on the vertical axis is time. The longer the period of time a user has to adjust to a supply restriction, typically the smaller is the consequence (substitution becomes easier). With a sufficiently long adjustment period, scientists and engineers usually can identify or develop a substitute