The term used to describe a classification tool that allows a person to distinguish between many objects with different characteristics (like birds, flowers, minerals, etc…) is a dichotomous key.  We started today’s class by defining the term “dichotomous” (separating into two contradictory groups) and then practiced constructing a dichotomous key by using an animal example. 

The example we completed in class involved separating the following six animals:  eagle, brown bear, ostrich, shark, polar bear, gold fish.  All six animals begin in one large grouping and we must divide them into two groups based on their characteristics.  Most classes chose to divide the animals into those that live mainly on land (eagle, ostrich, brown bear, polar bear) and those that live mainly in water (shark, goldfish).  We then broke each of those groupings down into smaller groups based on some other characteristic.  For instance, the land animals can be further divided into those that have fur and those with feathers.  The water animals can be separated by color.  The end result is a concept map (graphical representation) of an identification key that can then be used to identify each individual object based on its characteristics.

The lab that was completed in class consisted of constructing a dichotomous key to identify ten different types of clips:  butterfly clips, paper clips, binder clips, brass fasteners, etc…  The lab was due at the end of class and worth 15 points.

Next we will aim to identify 10 mineral samples by using a large dichotomous key that characterizes minerals based on those properties we defined earlier in the week:  breakage, hardness, color, streak, transparency, density, etc…

Homework:  Study for the mineral characteristics quiz on Thursday.