Google has made its stance against bitcoin and cryptocurrency mining applications in the play store. This includes non cloud based cryptocurrency mining applications only as there are certain apps in play store that let you monitor cloud based mining or your own mining setups.
Google now states that it does not allow applications that let you mine cryptocurrency on the devices. This has been included in the developer policies. Here is the exact quote:
We don’t allow apps that mine cryptocurrency on devices. We permit apps that remotely manage the mining of cryptocurrency.
On the flip side, you cannot gain anything financially by mining on a mobile phone. For any serious mining, you would need ASIC machine for bitcoin/litecoin or a powerful graphics card for equihash mining (Zcash, Ethereum, ETC).
Google has done a similar crackdown on various mining extensions that popped up in the Chrome web store back in april.
Keep in mind that Google is doing this not to prevent people from using cryptocurrencies, it is being done to prevent people maliciously inserting miners into free applications.
Back in March, Google had also announced that it would launch a crackdown on content advertising cryptocurrencies and bitcoin but later relaxed its stance.