As of the end of 2012, we now know of about 65 different meteorites from Mars with a total weight about 120 kilograms. Some fell as showers (e.g. Nakhla, Tissint), and some can be paired by common lithology, age and fall location, but it is more instructive to consider how they are grouped by "launch pairs". If you add the terrestrial age to the cosmic exposure age (CRE) you get the time when the meteorite was launched off of Mars by impact. Since only rather large impacts would do this, there must be a finite number of such impacts — hence grouping of samples.
Now that we have such a large number of samples, it is time to understand what we have and infer what we can about Mars. It's like putting a puzzle together were someone keeps adding pieces as you go along (see my Introduction 2006). Most Martian meteorites are mafic basalts. That is, they have an abundance of Fe and Mg,
are low in Si and Al and have a texture of intergrown minerals typical of terrestrial basalts (the tradition has been to call them "shergottites", after the first sample recognized as such). Some often have an abundance of large olivine crystals (so called olivinephyric). Others have an abundance of both high– and low–Ca pyroxene, with poikilitic textures and were originally called "lherzolitic shergottites". But it has now been recognized that there is a more fundamental and better way to describe these rocks (Irving 2012).
For further information, see: https://imca.cc/mars/martian-meteorites.htm
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