A circular button for Android. Apply the layout using android:background="@drawable/button_circular".

button_circular.xml

<?xml version="1.0" encoding="utf-8"?>
<shape
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle"
    android:padding="10dp">

    <solid
        android:width="3dp"
        android:color="@android:color/white" />

    <padding
        android:left="20dp"
        android:right="20dp"
        android:top="6dp"
        android:bottom="6dp"/>

    <corners
        android:bottomLeftRadius="25dp"
        android:topLeftRadius="25dp"
        android:topRightRadius="25dp"
        android:bottomRightRadius="25dp"/>

</shape>

<Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="@drawable/button_circular"
        android:text="Login with Twitter" />