The crystalline astro type was previously considered among the best astro types and coveted by players due to its very good crystal stat. However due to its low fertility, metal and area stats, as well as the fact that its high economy makes for a tempting target for other players to attack, it has fallen out of favor and is no longer as popular as it used to be.
The most coveted of all Astros (many players regularly try to buy and sell them on the forum - which is not allowed); despite the low fertility and area. They are used solely as economic bases because of their high crystal level. As well as having the highest crystal level of any astro, they are rare and quickly colonised by players which is why they are so coveted. Some players advocate getting as many crystalline bases as possible, but some think the compromise on fertility, area and metal (compared to a rocky astro) isn't worth the economic boost.